Alrighty my first post adding something back, many reading this will know about these already but hey ho might help somebody out.
1) Graphical disk space representation with Space Monger. Download - SpaceMonger 1.4
This program shows your hard drive usage as proportional squares which is great for getting a feel for your drive usage and for those "MY IPHONE BACK UP IS HOW BIG???" moments so you can clean some extraneous stuff up. It's an old version but it's free and works for Win 7 and Vista that I've used.
2) Power searching your hard drives with Agent Ransack. Download - Agent Ransack 2010
Agent Ransack is great as it power searches very quickly using multiple threads and searches deeply, it's also intelligent and has more options as far as searching goes and the parameters you use. For those of you who may have disabled indexing like myself it's also incredibly useful. Feature comparison
of the free version to the paid version.
3) Defragging your PageFile with PageDefrag (Win XP) - PageDefrag
For those still on XP who want have a fragmented pagefile and want it to get defragged quickly on a reboot without resetting the pagefile then use this. Otherwise if you're on Vista or 7 best bet is to redo your pagefile and set the min and max values the same as the system recommended value so that it doesn't fluctuate in size, and then move it to the faster beginning of your disk and there are many ways to do that.
These are pretty old and can be inconsequential to most but it can be a real help to the few who want them.