Depends on if you're considering an Si (K20) or a non-Si (R18).
Are you going for a "look at me" color or a more sophisticated, classy color?
Outside the Si's Fiji Blue Pearl and Habanaro Red Pearl, there really aren't too many "look at me" colors for the sedan, but a very well maintained and waxed Nighthawk Black Pearl could do the trick.
Personally, my favorite color on the sedans is Atomic Blue Metallic. I rarely see it, and waxed, it looks gorgeous. Galaxy Grey Metallic is nice when it is well maintained, but 90% of the GGM cars I see look like crap because the person driving it doesn't care about cars. It's also one of the most, if not the, most produced colors on the Civic.