If you don't like oscars, that's cool, there's lots of others to choose from. O's don't lose their colour and markings as they age unless they are being kept in sub standard conditions. If anything, both of mine have colored up even better with age. Homer...the big guy in my avatar is even brighter than that now. The old brute is over 13 inches and looks amazing (not bias or anything

). I am on my work cpu right now, but will have to post a pic of him sometime later.
One thing I'm not hearing as a suggestion is a male Green Terror. They can have a decent personality, and are extremely colorful and impressive to watch. Just look at that fella's avatar...posted at the bottom of page 2 (forgot his/her name). And although a common fish, a big male isn't as common as some think. Motas would be another cool option, and female festaes don't get too large and can look absolutely amazing (a shame that a pair isn't feasible in an 80 G). A pair of JDs would be beautiful, but don't make the best "Wet Pets". What about....hmmm, a big male Hatiansis is impressive. Trimacs are awesome, but males get a bit big for a 80G. Oh, something like a Synspilus would be pretty sweet too, and a bit out of the ordinary...zonatum too, anything of that genus. TUIC has several species available right now I think.
Whatever you choose, good luck, and post some pic's when it gets bigger
