(MONEY Magazine) – For wage slaves who strike out on their own, one of the toughest parts of leaving a company is saying good-bye to a 401(k). If you're among them, you may not have to miss out on this benefit anymore. Recently, a growing number of financial services firms have rolled out individual 401(k) plans, boasting many of the same features as their corporate counterpart. Entrepreneurs have responded enthusiastically: Solo 401(k) assets now stand at $2.5 billion, and could hit $90 billion by 2012.

It's easy to see why the plans are becoming so popular. As with ordinary 401(k)s, as well as SEP-IRAs designed for the self-employed, individual 401(k)s allow you to invest a portion of your income on a pretax basis—and your contributions grow tax-deferred. But unlike with a SEP, you can borrow against your account, plus the contribution limits are a lot higher. This year you can save as much as 100% of the first $14,000 of income, plus an additional 25% of your total compensation. By contrast, with a SEP you can only contribute up to 25% of compensation. (Maximum contribution for both plans this year: $42,000; $46,000 if you are 50 or older.) Says Jodie Hale, vice president at Pioneer Investments: "These plans allow people who work for themselves to stash away more money than just about any other retirement option."

An individual 401(k) isn't right for every small business. If at some point you might hire employees, look elsewhere, since you'd have to convert to a more cumbersome employer 401(k). The plans also don't offer a savings advantage over SEPs for high earners: You will hit the top contribution level for both types of plans if you earn $167,000 or more ($184,000 if you're 50 or older).

Still, for most one-person outfits, a solo 401(k) makes sense. Here's what to look for as you shop for a plan.

• Check out investment options. Unlike corporate 401(k)s, which often offer dozens of funds from multiple fund families, many solo 401(k) providers restrict you to one fund group. You'll find the widest range of investment choices at fund supermarkets like Fidelity and Schwab.

• Keep a lid on costs. Fees vary widely among 401(k) providers. Set-up charges and annual fees range from zero to $250 or more, depending on the amount of advice offered. Many firms, however, will waive some expenses for larger accounts. For example, T. Rowe Price charges $10 per fund but waives the fee for balances above $5,000; Schwab waives its $45 annual fee for accounts with $100,000 or more.

• Consider your borrowing needs. Although the law allows you to borrow as much as 50% of the assets in your solo 401(k), up to a limit of $50,000, not every provider offers a loan option. While it's certainly not advisable to raid your retirement plan for cash, many entrepreneurs and freelancers need the financial safety net that a loan feature provides.

• Get help. To jump-start your search, go online to 401khelpcenter.com, which lists nearly 100 individual 401(k) providers. Or ask your accountant or financial adviser for plan recommendations. After all, the sooner you can get a retirement plan in place, the better the odds that your nest egg will grow as quickly as your business.