I have a Palm m105/8Mb/PalmOS 3.5. I just use Google to find software but here's some tips (some might not work depending on OS and processor you have).
Easy Calc for a good scientific calculator.
CSpotRun for reading books.
Filez for a better file manager.
GrayPaint 2 for when you just need to be artistic on a Palm. Dunno, if you have colour.
IR-Pong 2 and
IRTris for humiliating your friends that have Palms. Well, IRTris is fun solo too.
LispMe for your programming needs.
Noah Lite for the dictionary/thesaurus, the best I know of.
Patience for solitaire etc.
SFCave for the simplest fun game.
X-Master for the hacks. I use AfterBurner for overclocking, AppHack to launch more applications from the keys, BatteryLog and Parentheses Hack (for LispMe).
You might also want to try
MessagEase for alternative input (faster).
I use
AvantGo at times to read a couple news sites. I would read my mail with some software but my old GSM doesn't have a modem.
Oh, share some hints, if you come up with something better

.