(FORTUNE Magazine) – 1 Michael Dell Chairman/Founder Dell Computer

WEALTH $17.95 billion AGE 39

Dell gave up his CEO title this year, but not his drive for tech-world domination. His wily advisors at MSD Capital helped boost his holdings by almost $1 billion in 2004.

2 Pierre Omidyar Chairman/Founder eBay

WEALTH $10.05 billion AGE 37

The eBay founder's net worth jumped $3 billion as a result of the company's stock surge. Meanwhile, he's created the Omidyar Network to invest in social change.

3 Jeff Skoll Chairman/Founder Skoll Foundation

WEALTH $4.69 billion AGE 39

Though he's no longer eBay's president, Skoll still owns 8% of its stock. Last year his foundation gave $8.2 million to found a center for social entrepreneurship.

4 Larry Page President, Products/Co-Founder Google

WEALTH $4.19 billion AGE 31

After selling only $42.5 million of Google's newly public shares, Page retains billions' worth of company stock. Meantime, he still lives in a rental apartment.

5 Sergey Brin President, Technology/Co-Founder Google

WEALTH $4.17 billion AGE 31

Google's technical wizard, Brin is also keeping his wealth in company shares. Meanwhile, Pravda named him one of the most famous Russians living in the U.S.

6 Jerry Yang Chief Yahoo/Co-Founder Yahoo

WEALTH $2.81 billion AGE 35

Yang LOL'ed all the way to the bank, thanks to a zesty rise in Yahoo's share price. His other investments, including a fistful of Cisco stock, helped.

7 David Filo Chief Yahoo/Co-Founder Yahoo

WEALTH $2.57 billion AGE 38

Filo stuck with Yahoo's shares, which make up virtually all his wealth, on their long way down--which made the 192% rebound since January 2003 all the sweeter.

8 Ken Griffin President/Founder Citadel Investment Group

WEALTH $1 billion AGE 35

The youngest of the rich hedge fund managers, Griffin made a bundle in convertible bonds and recently moved into energy trading.

9 Dan Snyder Chairman/Principal Owner Washington Redskins

WEALTH $823 million AGE 39

Snyder made money selling his advertising firm, then acquired the Redskins. In late August he bought eight million shares of Six Flags stock, giving him 9% voting power.

10 Marc Benioff* Chairman/CEO Salesforce.com

WEALTH $376 million AGE 39

Despite a snafu caused by his comments in the press, Benioff's customer-relationship management company debuted its stock this year and is now worth $1.3 billion.

11 Jeffrey Citron Chairman/CEO/Co-Founder Vonage

WEALTH $346 million AGE 34

Citron has made a habit of turning the low tech into high tech (see story in this issue), leading stock trading (Datek) and phone service onto the Net.

12 Elon Musk CEO/Founder/CTO Space Exploration Technologies

WEALTH $328 million AGE 33

The former PayPal wunderkind's eBay stock isn't the only thing heading into the stratosphere: Space Exploration's first rocket is set to launch this year.

13 Sean Combs (P. Diddy) Chairman/CEO/Founder Bad Boy Entertainment

WEALTH $315 million AGE 34

Producing, songwriting, rapping, acting on Broadway, running a successful clothing company--Combs is hip-hop's leading hyphenate.

14 Tiger Woods Golfer

WEALTH $295 million AGE 28

While the greens haven't been so good to him lately, the greenbacks keep flowing: AmEx pitchman Woods again leads all athletes in endorsement and appearance fees.

15 Halsey Minor Chairman/CEO/Founder Grand Central Communications

WEALTH $286.1 million AGE 39

The founder of CNET left in 2000 and started tech services firm Grand Central, whose value has nearly doubled, in part because of a deal with AT&T.

16 Shawn Carter (Jay-Z)* Co-Founder Roc-a-Fella Enterprises

WEALTH $286 million AGE 34

Hit rapper Jay-Z not only delivers platinum albums but also owns half of Roc-a-Fella, which produces records, "urban streetwear," premium vodka, and ice cream.

17 Jerry Greenberg Co-Chairman/Co-CEO/Co-Founder Sapient

WEALTH $278 million AGE 38

With Sapient's stock soaring of late, Greenberg is worth more than double what he was two years ago. But he's still far below his $1.5 billion peak in 2000.

18 Raul Fernandez Chairman/CEO ObjectVideo

WEALTH $263 million AGE 38

After Fernandez sold tech services firm Proxicom in 2001, he tried retirement and philanthropy--and then joined ObjectVideo, a private video-surveillance software firm.

19 Jennifer Lopez* Actress/Singer/Co-Owner Sweetface Fashion

WEALTH $255 million AGE 35

Gigli may have bombed, but Lopez's perfume and fashion line, sold in department stores, had a boom year with $300 million in revenues. Her latest: a lingerie line.

20 Marc Andreessen Chairman/Co-Founder Opsware

WEALTH $253 million AGE 33

The original Internet millionaire (remember Netscape?) now heads Opsware, a provider of "data center automation software." Biggest clients are NEC and HP.

21 Joe Liemandt President/CEO/Founder Trilogy

WEALTH $234 million AGE 36

A Stanford dropout, at age 21 Liemandt used credit cards to start Trilogy. While web spinoffs like Carorder.com failed, selling e-business software to Boeing and IBM hasn't.

22 Shaquille O'Neal Basketball Player Miami Heat

WEALTH $222 million AGE 32

Getting traded to Miami hasn't affected the big man's endorsement contracts. Living in a state with no income tax won't hurt his finances either.

23 Michael Robertson CEO/Founder Linspire

WEALTH $220 million AGE 37

Robertson used millions from selling MP3.com to start Lindows, a Linux-based competitor to Windows. The name was changed to Linspire after Microsoft squawked.

24 Marc Ewing Publisher Alpinist magazine

WEALTH $217 million AGE 35

The founder of tech IPO star Red Hat, Ewing left and started Alpinist, an award-winning magazine devoted to mountain climbing, one of his favorite pastimes.

25 Julia Roberts Actress

WEALTH $212 million AGE 36

Still the highest-paid actress in Hollywood, Roberts landed a $25 million deal this year for the forthcoming movie Closer, directed by Mike Nichols.

26 Will Smith Actor/Rapper

WEALTH $188 million AGE 35

Though Smith has vowed to stop making big blow-'em-ups, his I, Robot payday was reportedly $28 million. He took a pay cut for the forthcoming Shark Tale.

27 Andre Agassi Tennis Player

WEALTH $162 million AGE 34

Agassi may be ancient by his sport's standards, but he continues to win tournaments--he's second in all-time tennis earnings--and endorsements.

28 Jared Polis Chairman/Member at Large Colorado State Board of Education

WEALTH $160 million AGE 29

Polis's ascent began with the sale of e-card company Bluemountain.com and continued with an IPO last year for Provide-Commerce, the parent of Proflowers.com.

29 Jeff Gordon* NASCAR Racer

WEALTH $155 million AGE 33

Not only is Pepsi and FosterGrant plugger Gordon the biggest advertising earner in NASCAR, but he's also a 50% owner in his Nextel Cup--winning racing team.

30 Sudhakar Ravi Retired

WEALTH $137.1 million AGE 39

Ravi retired from SonicWALL, an Internet security operation, in 2002. Now he's training for a triathlon, learning golf, and spending time with his three tots.

31 Ashley Olsen* Actress/Co-President DualStar Entertainment

WEALTH $137 million AGE 18

The sisters worked for scale as 9-month-olds but now are co-presidents of a billion-dollar company, shooting 47 direct-to-video titles and two feature films along the way.

31 Mary-Kate Olsen* Actress/Co-President DualStar Entertainment

WEALTH $137 million AGE 18

Like her sister, probably the wealthiest self-made college student in the country, with a Wal-Mart clothing line and a set of dolls sold by Barbie behemoth Mattel.

33 John MacFarlane CEO Sonos.com

WEALTH $136 million AGE 38

MacFarlane got rich at OpenWave, whose software manages telecom data. In 2002 he started Sonos.com, which makes digital home-music equipment.

34 Jeffrey Zients Chairman Advisory Board Co.

WEALTH $132 million AGE 37

Zients not only leads Advisory Board, a health-care consulting firm, but also runs Portfolio Logic, which invests in business services and health-care companies.

35 Sreekanth Ravi Retired

WEALTH $131 million AGE 37

Like his brother, Sreekanth Ravi retired from SonicWALL to pursue the good life--scuba diving, a baby, Southern France--and is now planning a new Internet company.

36 Paul Gauthier Retired

WEALTH $129 million AGE 32

The co-founder of search engine Inktomi cashed out early, before the company was bought by Yahoo in 2002. He remains retired and out of the public eye.

37 W. Glen Boyd Retired

WEALTH $125 million AGE 37

Boyd sold Net analytics company WebTrends for a reported $1 billion in 2001. These days his foundation donates to environmental and other causes.

38 Britney Spears* Entertainer

WEALTH $123 million AGE 22

Tireless touring has raked in more concert revenue of late than even Madonna's. Plugs for Pepsi, Clairol, Polaroid, and others suggest she's the new Material Girl.

39 Michael Saylor Chairman/CEO/Founder MicroStrategy

WEALTH $113 million AGE 39

One of the Net's original cowboys rode the bucking-bronco stock of software provider MicroStrategy from $6 up to $330, then down to $10 and back to $30.

40 Kevin Garnett* Basketball Player Minnesota Timberwolves

WEALTH $106 million AGE 28

In 1997, Garnett signed what was then the most lucrative deal in sports, $126 million over six years. The NBA MVP also started his own clothing line in 2002.

*New this year.