Well since this turned into a length and color discussion, frankly I love longer hair, but certain shorter styles can get me going.
As for color, my top five single colors are pink, white/silver, blonde, black, and blue.
Some color combos I've found that normally (depends on the style a little bit) work pretty well are white+bright red (one of my favorite combos. I'd actually put this above pink), black and blue (my hair currently), black and white, blue and green.
For those who haven't already guessed, or just know me, I have a HUUUGE hair fetish. ^^;