I'm a fan of the Colorado Children's Immunization Coalition, whose purpose is to make sure my home state's kids are healthy and not susceptible to preventable diseases (they're on Twitter, too!). Last Thanksgiving, they had a "Thanks-a-thon", letting Coloradans post their messages and stories about their kids. It's a great read, with lots of heart-warming -- and some harrowing -- stories.
And while I'm at it, here is a great immunization FAQ posted by the American Academy of Pediatrics. In it you'll see something very hard to find on the web: actual science-based facts about vaccinations, without the scare tactics employed constantly by the antivax (what some people call the pro-disease) crowd. If you're wondering about getting yourself or your kids vaccinated, please check out that site and read it carefully. You may be saving not only your child's life, but the lives of other children as well.