Reindeercam.com shows a live feed of Santa's reindeer, and 3 times a day Santa himself comes out to feed them! Very exciting for the little ones. You can donate a dollar to help feed the reindeer, as well as have your child's name added to Santa's "nice" list. You can also mail a letter to Santa and get added to the list.
Portablenorthpole.com allows you to create a personalized message from Santa for free. Santa takes you on a little tour of his workshop and you can upload photos of your kids, which are included in the video. Even though she's only 19 months old, Francie was completely fascinated. The look on her face when Santa addressed her personally was just too sweet. You can also buy personalized items like books and letters. I really wish something like this had been around when I was a kid!
MaginSanta.ca is another site that lets you make a personalized video message from Santa. Not quite as nice as Portable North Pole, just because they had fewer options for names, but still very cute. (It doesn't recognize "Francesca", so I was stuck going with "Francia") It's definitely worth checking out.
Northpole.com is an interactive website that is geared more towards kids old enough to use the computer. It has a lot going on, so you can spend some time checking out all the features. You can make personalized stories, chat with Santa's elves, send letters to Santa, and more.