It really depends on what type of theme you want in the tank. When you decide on a broad theme, you can fit in the fish that would go well with each other. For instance, you could set up an amazon tank with lots of small tetras, like Neons, Glo-Lites, Serpaes, maybe Blackskirts. If you want just a couple larger fish you, could fit a pair of Blue Rams in the tank, though I don't think Angelfish would fit in there.
What type of decorations are in the tank? Planted? Driftwood? Rocks? All fake stuff?