I always find this question impossible to answer because I often don't know enought about what the brewer likes to brew, stylewise.
If you like American styles, Cascade and Centennial will get you far. A good clean bittering hop like Magnum, Nugget, or Warrior.
I brew lots and lots of English styles, so I salivate over EKG, Fuggles and Willamette. Galena as my high AA bittering hop.
For Belgians, Styrian Goldings or Saaz.
Williamette does double duty in lots of styles.