I'm a big fan of Columbus or Chinook for bittering IPA.
I have also started to use Nugget quite a bit as well. It doesn't give quite as much of a bite as Chinook or Columbus, but it's not as neutral as something like Magnum, either.
For flavor/aroma hops my favorite combos have been:
Simcoe, Amarillo, Citra
Amarillo, Columbus, Ultra
Citra, Amarillo, Mosaic, Motueka
Caliente, Centennial, Amarillo, Motueka