There are 50,000+ apps, you can sort the Android market by "highest rated". You'll find the best out there, don't worry about it.
Also you can "return" purchases within the first 24 hours, so I would suggest only buying one app a day, so you'll have the most time to throughly test it before deciding on whether to keep it. Some apps don't work too hot on some devices. Also some apps do not come with trial versions.
The free apps I use are:
Barcode Scanner
Amazon
Notes
Mileage
Andoku
Replica Island
Blow Up Lite
iDemolished
Paper Toss
Toss It
Puzzle Lords
Abduction
Tetris
Monkey KickOff
Google Sky Map
Tapatalk
Movies
Key Ring
Facebook
FIOS Mobile
Mileage
EStrongs File Explorer