Absolutely. You don't want to put two dwarf or large Angels together, but they will get along fine with most other fish. You can mix Tangs, but it is best to mix body types, again, they will go well with most other fish. Tangs should be added at the same time, ideally. I do not have much experiences with butterflies, but have always heard that they do best in established tanks.
Places like liveaquaria have compatability charts too. Look at that and pay attention to recommended tank sizes for any fish you consider . LIveaquaria tends to suggest larger than other sites, but I tend to agree that their suggestions do better for fish.