I have 2 oscars, and obviously, they go well with another tankmate BUT only if they've grown up together (mine are siblings).
A good fish to be with them are plecos, although my oscars gave it a really hard time before (now the pleco has outgrown the oscars, so no more teasing!)
my 4 1/2 inch oscar is constantly bullying my 12 inch pleco lol..i think he must think he is bigger....