If you've decided you want to go with cyprinids there are a lot to choose from. Tigers are known for being on the nippy side of the coin, and zebras are known for being a bit manic. There are calmer relatives of both. Both are popular fish. Depends on what you want. I have dwarf barbs and two different types of rasbora, all of whom school. Nice fish, fairly mellow.
Green Tiger Barbs are just a color morph of the regular kind -- they're the same species and will school together. Tiger Barbs are generally better in groups. A few may be aggressive towards other tankmates,a few more and they'll direct more of their attention towards each other.
Gouramis are territorial fish and can be aggressive. They are close relatives of bettas and exhibit similar behavior. My male pearl gourami runs the tank, especially when bubblenest incidents are going on. I wouldn't put more than 1 male trichogaster in with 1 or 2 females. The female is pretty mellow. Dwarfs may be different, don't know as much about them, have heard they are prone to health problems.
Gouramis are also a fairly slow moving fish with long fins and those big whiskers. Boisterous fin-nippers like tigers may not be a great mix with them, although as RedRf noted, they can be quite fierce if provoked. Might work fine, might be a problem.
Some moderately sized loaches would make a nice bottom fish (clowns will eventually get to be too big for a 55). Loaches also generally like being in groups and like to play together. Mine are some of my favorites.