Depends how portable you want them to be, there are many headphones which are quite easy to drive...
Sony MDR-EX71 for canal phones are meant to be a good match, but if you want to go up more you can use Shure's or Etymotics.
Full sized headphones, the Grados will have no problems being driven, the Sennheiser HD497, PX100/200/250, HD515/555/595 should all be fairly easy to drive.
Beyerdynamic DT250-80, DT770-80, DT440/660/860.
Most Sony's are easy to drive too, Sony MDR-CD380, 580, 780, 1700, 3000.
What is your main taste in music?