Discus need to be in groups of 4 or more, and just a single discus would grow to big for a 29 gallon.
Guppies, platies, mollies, etc., are livebearers, so you would soon have too many- they provide terrible nutrition when fed to other fish.
Just and idea that I'm working on~
When my goldfish move to their 90 gallon, I'll be putting my current 10 gallon residents in my 29 gallon (read my signature).
Then I'll add a few other fish, and these will be my final stocking levels:
6-9 Glowlight Tetras
2 Peru Orange Stripe Corydoras Catfish
2 Albino Corydoras Catfish
2 Panda OR Corydoras A. Catfish (non-albino cousins of albinos)
2 Bolivian Rams
2 Milk & Ink Platies
1 Sunset Platy
Total= 17-20 Fish
The cories provide a bottom layer of fish, the rams are lower/midwater fish, and the glowlights and platies are midwater/top water fish.
I plan to plant it with the plants currently in my 10 gallon (Java Fern, Corkscrew Vallisneria, Vallisneria Americana, Wisteria, and Rotala Indica). I will also add a nice piece of driftwood I picked up when I got my 90 gallon, plus some decorative fish-safe rocks, and I'll probably add a lotus and microswords.