Champions Online has a training room called the Battle Station (check out NET Custa's video). It's pretty much a Danger Room, that you can set up with Enemies that you'd be running into. As you level up the enemies change to fit the type of enemies you'd be fighting at that level.
You pick the type of enemy group you'd be fighting (The Purple Gang, Demons, Irridiates, etc etc), then you choose the difficulty. Easy are for enemies 1 level lower than you, normal is for enemies equal level to you, and hard are for enemies one level higher than you.
Then you choose your team size. This is great if you want to practice with a teammate, or a regular group of guys. It also let's you test your solo ability.
My highest level player has been in the Training room for weeks, as I've been trying different in-style combinations (I mean, powers that fit his character). The one thing I noticed most was that my two favorite defenses are Regeneration and Invulnerability. Further more, don't forget you can pick an offensive and a defensive passive ability.
The Battle Station is an amazing room, and it can really help you decide what's best for your hero.