1. Superman Monti- there's a lot of look-alikes out there, but if you get the "original" superman, and get it in good conditions (even just decent conditions), its colors just POP.
2. Strawberry Shortcake/Shades of Fall/Red Planet- I group these together because, even though I have a frag of each, they all have similar overall coloration but different structure and shades of color- very nice though.
3. Sunset Millepora- orange base with green polyps- stunning! Plus you don't find too many orange SPS out there (also see sunset montipora)
4. Pink Lemonade- when these grow out to colonies, they look very nice.
5. Blue Hawkins Echinata- very cool coloration and growth pattern
6. Ponape Birdsnest- nicest birdsnest in my opinion
7. Blue Oregon Tort- can beat the blue on this.
8. Sapphire Blue or Palmer's Blue Millepora- very cool blues and greens/teals
9. GARF Bonsai- purple with neon green polyps
10. $500 Efflo- cool growth pattern and nice coloration.
Honorable mentions- dozens of other milleporas, Ice-Fire Echinata, Sunset Millepora, and A. Tenuis (gets great polyp extension).