NEW YORK (CNNMoney.com) - While the "official" start to the 2005 holiday shopping season kicked off for most retailers on "Black Friday," or the day after Thanksgiving, online merchants have their banner day on "Cyber" Monday.

Cyber Monday, the Monday after Thanksgiving, is quickly becoming one of the biggest online shopping days of the year.

According to the Shop.org/BizRate Research 2005 eHoliday survey released last week, 77 percent of online retailers said their sales increased substantially last year on the Monday after Thanksgiving, a trend that is expected to drive serious online discounts and promotions on Cyber Monday this year.

"On Cyber Monday, consumers set their sights on surfing for holiday gifts and shopping online," Scott Silverman, executive director of Shop.org, said in the report. "This year, online retailers will be capitalizing on the increased traffic by offering special promotions and discounts."

More than one-third of the 1,890 consumers surveyed for the report said they will use Internet access at work to browse or buy gifts online this holiday season. More than half of young adults the ages of 18 to 24, and nearly half of those aged 25 to 34 said they would shop online during work hours.

Among the most-shopped categories last year on Cyber Monday were jewelry, consumer electronics, gourmet food, furniture and home décor, the report said.

Total holiday online sales for the key November-December shopping months are expected to grow 24 percent this year to more than $19 billion, according to market research firm comScore Networks.

The Shop.org/BizRate report said many online retailers are planning to offer extra incentives on Cyber Monday, ranging from free shipping, to gifts with purchase, to deeper discounts.

"Once the parades have ended and the leftovers are put away, many consumers will find a few precious hours to get a jump-start on the holidays by shopping online," said Chuck Davis, chairman of Shopzilla, said in the report. "This year, retailers will be reminding shoppers that even though their stores may be closed, their Web sites are always open."