Ill start. Fish- the oscar. Every store i go to they say oscars are extremely aggressive and will kill anything in the tank. No they dont they will eat anything small enought. On rare incidents they can be very aggressive.
Plecostomus (most all ones sold at almost all pet stores, common and similar) as algae eaters and good community/pet fish. Only fairly good algae eaters for a little while and get gi-normous/too big for the average persons/fish keepers tank.