Software you should own (maybe)
I finally broke down this week and bought a copy of Partion Commander (I was actually looking for Partition Magic, but the store didn't carry it). I was trying to resize the partition on my hard drive so that I could install another version of Windows on the new partition. It's something that I find myself wanting/needing to do often enough that I should have just bought the software a while ago, but infrequently enough that I've put it off for a couple of years. Which leads me to thinking, what other pieces of software are like that? Something you really should buy but nobody really wants to? Off the top of my head the most important one would be a good anti-virus program.
There's another class of similar things which are 'software that's really useful and you should pay for it but it's unlimited beta or shareware'. WinZip was the classic example that very few people I knew ever bothered to register and pay for, but they used it all of the time. Other ones that are more relevant today would be the anti-spyware programs around (Spy-bot Search and Destroy, Ad-Aware, etc.).
On a tangent, since I've mentioned AV programs and anti-spyware programs, you should go try out the http://safety.live.com site - it's a new service that Microsoft is offering that will scan your computer for malware, checks your hard-drive to see if it should be defragmented, etc.