Ibanez tube screamer. not the shitty grey one. I'm talking the green expensive one. The turbo one doesn't have many usable sounds, so stick with the original....if you can get an old tube screamer that would be ideal.
There are a bunch of good overdrive pedals, there are SOME i can't recommend:
Boss, Danelectro (I'm sorry Richard!), or Digitech.
To me , the boss super overdrive just isn't as good as a tube screamer, and the daneletros ive used has been good pedals up until they broke...and they break pretty easily. Digitech pedals don't do it for me either. Overdrive/distortion is VERY complicated...and I believe some of the more expensive analog designs will improve your chances of getting a sound you'll like.
Hope this helps a bit!