What sort of characters do you like? What kind of movies do you like? There's a comic book for everyone, but its finding the right genre for you.
You could always try looking for cheap graphic novels on eBay or Amazon. Pick something you just like the look of, pick it up cheap, you've got a whole story in one book, and if you like it then you have a good starting point... if you don't like it, you wont have spent much on it.
Actually, you can find some in libraries too. That's even cheaper ;)
@dannymalt: I hated Batman Broken City. The world's greatest detective didn't actually detect. He ran around the city, getting beaten up by a little girl and was out-witted by Killer Croc. It was a crock alright.