Being that you have a small sized tank, larger sized fish would not be recommended! Tangs, Angelfish, with the possible exception of the Dwarf(centropyge) species, though with corals they are not recommended either, Grouper, most Wrasse species just to name a few should be eliminated from your wish list.
Having said this, their are a plethora of suitable community fish that remain small and perfect for a tank your size.
Clownfish can pose a problem as you need to be careful with aggression. Cousins of the Damselfish, they to possess the same territorial traits therefore,it is best to purchase a single Clown, or a pair, if you truly know that it is a pair.
Even more suitable to your size tank are, and this is just a small list, are:
Clown Gobies
Randal!'s Goby
Black moon Goby
Fire Gobies
Lawn mower Blenny
Midnight Blenny
bicolor Blenny
Starry Blenny
Six Line Wrase
Fairy and Flasher Wrasses
Pajama and Banggai Cardinalfish
Cleaner Wrasse
Chromis'
Damselfish like the azure, Starks, demoiselles , yellow belly
this is a small sample to get you off on the right foot.
As for the Tridacna Clams are concerned, Derasa and Squamosa would be your ideal choice. Easier to maintain due to light restrictions. They are not as finicky as would be the case with Crocea and Maxima.
