The official website for Borderlands 2 now has a skill tree builder for all four playable characters: Axton, Maya, Salvador, and Zero. To access the trees simply go to the main site, click 'characters' at the top, and then choose which character you'd like to explore.
Borderlands 2's skill trees work very similarly to the original game; you choose your primary power and then can begin going down three separate trees with several tiers full of enhancements and abilities. However, compared to the original title, Borderlands 2 will offer you a little more bang for your point invested, and there are two additional tiers to unlock.
If you have a chance be sure to look at the skills for the character you're planning to roll and compare them to the others. Maybe you will find out that there's another character with even more enticing options for you.