Tiefling is in 3.5 and in a core rule book Monster manual I. It's not overpower. The benefits of the race really isn't worth the +1 level adjustment. I think people only use because they want to be a Tiefling. As for me classes I would like to use one of these base classes Ninja, or Swashbuckler. Ninja is in Complete Adventurer, and Swashbuckler is in Complete Warrior. I can't really find a link to those classes just up on the web anywhere. All I could find are ninja classes that people made themselves, and those are over powered.
One a side note you should really look into getting the Complete books as pdfs there are a lot of cool classes, prestige classes, and feats in them.
ultha is right on the matter of tieflings not being overpowered for races. In the monster manual 3.5 they are listed under the term planetouched. And basically they get a few powers. Heres the SRD upon the subject.http://www.d20srd.org/srd/monsters/planetouched.htm#tiefling
Tieflings As Characters
Tiefling characters possess the following racial traits.
+2 Dexterity, +2 Intelligence, -2 Charisma.
A tiefling’s base land speed is 30 feet.
Darkvision out to 60 feet.
Racial Skills: Tieflings have a +2 racial bonus on Bluff and Hide checks.
Racial Feats: A tiefling gains feats according to its class levels.
Special Attacks (see above): Darkness.
Special Qualities (see above): Resistance to cold 5, electricity 5, and fire 5.
Automatic Languages: Common, Infernal. Bonus Languages: Draconic, Dwarven, Elven, Gnome, Goblin, Halfling, Orc.
Favored Class: Rogue.
Level adjustment +1.