Depends on what fish you want to keep and what size they are.
I'd probably only keep one Oscar in a tank that size but i might go for over 100 guppies.
The secret is balance....i had a tank exactly the same size as that and i had 5 clown loach, 6 corydorus catfish, 30 rummynose tetras, 20 harliquins, 4 angelfish, 2 pearl gouramies, 3 plecos, 1 RTB shark and 4 swordtails.
That gave me a balance of colours, a couple of nice shoals, some bottom feeders and a few "feature" fish. There was 75 odd fish in there but it didn't look over crowded. The tank was very heavily planted too.
A good aquarium forum i've used for the past 5 years is
http://www.uk-aquarist.com/index.php?&act=idx it's well worth subscribing and asking on there.
Good luck