I have 5 full screens of apps, and I have never paid a cent for one! Check the “Top 25 Free” list in the App Store. It updates several times a day, and shows the movers and shakers in free apps. Also, a lot of paid apps make their debut as free ones, and you can grab yourself a free copy. I’ve gotten White Noise, Air Sharing, earthscape, Break Classic, and Fuzzle this way.
I personally think that “Stanza” is the best app, free or paid, in the store. It’s free. Also, check out these essentials:
GraphCalc
Instapaper (great for ipod touch)
Evernote (if you use it. you should!)
Twinkle
Tap Tap Revenge
Frotz
Constitution for iPhone
Now Playing
Check those out and let me know what you think.