What functionality are you looking for? There are tons of free programs out there, but even when you get into commercial software, most PalmOS stuff is $25-50 so it may be worth the money to get what you need.
Something simple, but a little more advanced than the one that is included witht he Palm software. In other words, I would be able to place a good amount of info on each hour that I have something to do. The one with the Palm OS limits your time and space.