I just spent the last month of holidays going over every category of app/top 10 lists/recommendations, finding the best ones. I have about 100 'must have' apps that don't include games/website + company apps/gimmicks, I'll post the list when I'm done... I'll just post 10 that are nice:
Google Sky -see all the stars
Satalite AR -see all the satalites
Network Spoofer - troll starbucks
Aard - offline wiki's
Terminal IDE (replace regular terminal) - run Vim on your android from your desktop
AndroIRC - real men's internet chat
Ivona Voice beta
LBE - the only real 'must have' app (security)
and 2 games:
Droidfish -chess
Counter Strike