some great choices that will get along are:
clowns - as you suggested you want
dottybacks are a suggestion - unsure of pricing out that way though; a royal dottyback or strawberry dottyback; nice little fish.
triggers are a no go altogether unless thats all u want to have in the tank!!
for a 55 gal
i'd suggest 2 clowns, a dottyback, a goby of some sort, a firefish, maybe a shrimp and a dwarf angel (flame is a hardy little guy)
but as kat said damsels are very territoral.. if u do end up getting them, introduce them LAST!!