plenty. dont mix nw with african. dont mix mbuna with lake. etc etc. and of course there is also the dont put two males together, especially if there is a female present. the list is endless. then you have the overstock the tank so there is less fighting theory. the cant add one fish to a tank without rearranging the entire thing (and im not imaginative enough to come up with different designs every time). and so on and so on.
there are a ton of cichlids that dont get along. i am just starting to get into them and with as much as i have learned in the past few months, i feel like i still have little to no real knowledge. i just go an lfs near me that does mostly cichlids. i ask the employees tons of questions. and i watch the tanks to see who is getting along with who. then i remember that just because i see these fish live together, it doesnt mean i will buy some that will.
but, even with all the compatability issues and concerns, i still think they are some of the coolest fish out there. so i continue to try to muddle my way through. thankfully there is this website to help me along the way. i know this probably doesnt help you much, but i took the oppurtunity to spew forth some of my verbal diarrhea.