Hitman Pro
http://members.home.nl/mloman/hitmanpro243.exe
This is a very handy anti spyware program. It's already very popular in the netherlands (it's developer is dutch). It's a shell around a couple of programs like spybot, cwshredder, ewido micro, ad aware and alot of others. You can completely customise the programs you want to run. I recommend customising everything because it might do some stuff you don't want. And if you press start it completely does everything for you even accept the license agreements if you want. The only disadvantage is that it takes alot of time to run because it runs alot of seperate anti spyware/virus software.
Regcleaner
http://www.worldstart.com/weekly-download/programs/regcleaner.exe
regcleaner is a very small registry program. You can clean up your computers registry alot with this and edit the programs that load on start.
Editpad lite
http://download.jgsoft.com/editpad/SetupEditPadLite.exe
editpad lite is a replacement for the standard .txt editing program in windows notepad. It practically the same for some extra's and it looks a litte different. It has tabs, you can redo and undo as many time as you like, you can edit html much better in it and it can open much larger files than notepad. There's alot more but those are the most important.
Nlite
http://nuhi.olmik.net/new/nlite1.0fi.exe
Nlite is a program with which you can edit your windows xp cd. You can add service packs and hotfixes. integrate some usefull programs and remove alot of windows crap you don't want or need. You can also edit alot of options you usually have to do after you installed windows. This saves alot of time if you reinstall your windows especially when you need to do it on several computers.
Here you can find the updatepacks and other programs to integrate into your windows cd:
http://www.ryanvm.net/msfn/updatepack.html