my 2 cents:

- TreeSize ( and/or SequoiaView ) -- see where the big files/directories are on your harddrives

- Piriform CrapCleaner -- deletes unwanted/unneeded files after booting; configure all of it, then add folders and log files manually (find good candidates with Treesize ;) I like all Piriform tools, they're small, quick and slick. I wish they made more things.

- any SysInternals stuff you have a use for (Autoruns is a must have)

- DirectoryOpus -- the best file manager I know

- FreeFileSync -- backup/synchronize directories (locally, that is). Can also monitor directories for changed stuff (also for Mac and Linux)