Have you read up on fishless cycling? I'm sure you have, but there is an article about it on this site.
Maybe it would help you to decide what you want to test the pH of your water. If you have a really high pH, that would be perfect for Africans. If not, you would do well with South or Central Americans. Or, if you wanted to try to get your pH up, you could go for Africans anyway!
Have you checked out
www.liveaquaria.com ? I hear they are a very good online retailer (although kinda on the expensive side), and they have a live arrival guarantee on their fish. You can order plants from them too. Even if you don't want to order online, check it out because they have profiles on their fish and could maybe help you get an idea of what you want. Also, you could look around at
www.cichlid-forum.com at their cookie-cutter setups for 55 gallon tanks. They have these for African and New World cichlids.
55 gallons is a great size for cichlids. Sure, there are some that you still can't keep due to their size, but you still have a ton of options for a very interesting tank.