Jeff Atwood makes a great point. If you read the comments of the post, and I do recommend it, you can get a lot of great little pieces of software. Granted most are aimed at programmers, but still worth the look. Like Jeff, I also registered WinZip back in the day when they shipped it on a 3.5" disc even if you downloaded it at no extra charge.
I tend to use a fair amount of Open Source software. Many times I find Open Source or shareware tends to get the software that I need and they respond well to bugs or exhancements. I prefer Open Source since if something happens to the primary developer the project is still there for someone else to pick up. I have run into problems with shareware when the developer has some problems (or worse yet, dies) and there is no one to pick up the project.
I registered MPG, a small Palm app to keep track of your milage and total cost of ownership for multiple cars. I have used it for years but never paid for it, just putting up with the nag screens.
Some others I will be registering are Euchre, a Palm-based Euchre game, plus sending some money to the nice people at Mozilla for FireFox and ThunderBird, plus digging through my pile of programs at home to see if I have been negligent in the past.
Some other programs I have registered - FeedDemon (RSS reader), TextPad (fancy text editor, primarily for programmers), Geocaching Swiss Army Knife (handling GPX files from Geocaching.com), Cachemate (Palm-based handling Geocaching info, works with Geocaching Swiss Army Knife) and Runners Log. Those are the biggies.
Update: Ooops. Runners Log can be found here.