As others have suggested to me, look into an angelfish pair, or ram pair (bolivian or GBR). You can also make an angelfish species tank and make it amazonian themed. Also look into psuedomogil gertrude, my favorite rainbow fish. ^^ Try to think of a theme or set of colors you'd like if it helps. I'm planning on making my 10g a reddish tank with ember tetra and honey gourami.