Nick Jr. (http://www.nickjr.com)

There are very few preschool-targeted sites that rival NICKJR.COM's quality content. The games are fun, age-appropriate, and educational, with obvious tie-ins to Nick Jr. TV characters that most preschoolers are already familiar with. There's a great video library that shows kids how to make fun snacks or clean up the beach. And the excellent parent section has lots of activities to print and do offline.

That said, this site is also one big advertisement extravaganza. In addition to the slew of commercial kid- and parent-targeted ads that pepper the site, you'll also encounter Nick's own ads, plus links for the Nick web store, cruise, resort, game arcade store, and more. It's a trade-off, but overall the site's content is worth it if you can ignore the sales pitches (some parents also choose to install ad-blocking software).