Gearbox has just come out with an online tool that lets you mess around with some of the skill tree stuff for Borderlands 2 before it comes out. Although I'm not overly interested in this particular game I find this idea really exciting. I think Saints Row did something similar. It's something I've wanted in gaming for a long time.
I'd love to see pre-release character creation tools for games. I think if these tools were available for download ahead of release publishers might even snag extra sales if a bored gamer tries it out and becomes attached to their new avatar. It would also be super handy if you're like me and spend WAY too much time fussing over every detail before you actually get into your game.