Mini Bio Section
Since your About page is about you and your blog, it's probably a good idea to include at least a little section giving people a mini bio of yourself. You can include what you blog about, things you like, where you are in life (student, married, mother, etc), your career, where you live (if you feel comfortable disclosing your general location), and so on.
F.A.Q. Section
A great thing to include in your About page is an F.A.Q. section. Oftentimes you'll get a lot of the same questions asked of you and by including the answers to those types of questions in your F.A.Q. you can avoid having to answer it over and over. You can also use formspring or a general call for questions people would like answered to find questions for your F.A.Q. You might discover some things people were wondering that you'd never thought to share before!
Favorite posts
I like to include links to some of my favorite or most popular posts, so if people are just starting to read my blog and might have missed some of my favorite posts from the past, they can check them out! On my blog, this is actually on a separate page from my About page-- my Start Here! page, which I created as sort of a mini About for people who've just discovered my blog.
Info for sponsors
Potential sponsors will often go to a blogger's About Me page to find out more about how they can sponsor. It's good to include a link over to the page you've created with all your sponsorship info, so potential sponsors can find the information they're looking for.
Your contact info
Don't forget to let people know what your contact info is! Make sure to include your email address and if you haven't elsewhere on your blog, link to your blog's facebook page and twitter.
Fun pictures!
Because reading a huge block of text is no fun. Include some fun photos of yourself (this is, after all your about ME page. Haha!)