The Thanksgiving shopping marathon continued on Monday as virtual crowds swarmed online merchants in search of Web-only specials, discounts and free shipping. After the drop off in healthy in-store sales and foot traffic on Black Friday, many retailers slashed prices and offered Web-only promotions to boost their business as the weekend progressed.

In fact, online retailers dangled more free-shipping offers and bigger discounts to get shoppers clicking on Cyber Monday - which marks the start of the online holiday shopping season. Specials included 25% off watches at Kmart.com and up to 60% off toys and games at KBtoys.com. Along with up to 50% off tools, Sears.com offered free shipping on orders of $49 or more.

Keynote Systems Inc., an Internet consulting company that helps companies improve their Web sites, reported that consumer traffic was so heavy that JCrew.com went down for a few hours, Gap.com for a brief period and Staples.com’s site slowed.

According to Andrew Lipsman, senior analyst at comScore Inc., which tracks online spending, “I don’t think there’s any doubt that the promotions being offered online are significantly more aggressive than we’ve seen in the past. It’s almost really standard to offer free shipping at this point. They’re doing what they need to do.”

The Cyber Monday sales are closely watched since it is the first day after the Thanksgiving weekend when workers get back to their offices and start shopping at their computers for holiday gifts. The results typically provide a barometer for how the rest of the online holiday shopping season will unfold.