I'm using the following:
Type: Diagnostic, Security & Safety:
HD-Tune for finding disc-errors
TrueImage for Images of my HD (50€)
VMWare for testing viruses, testing programmes before installing them on my "real" system or for only temporary use and similar. Use the 30 day evaluation-version for installing a system and use the free VMWare Player to work with it.
Sandboxie to install tools I'll only use one time, because I can delete it completely with minimum afford (registry-entries are saved to a dat-file). Is also usefull for browsing.
HD-Graph to find big amounts of space if my HD get's full
Unlocker to find the process using a file that can't be deleted. It can unconnect the process or kill it.
Netmeter to have my traffic always in a little window onscreen.
TrueCrypt to crypt parts of my HD.
Type: Internet
Hamachi to play LAN-Games via I-Net.
Type: Multimedia
MP3Tag to (multi) change the tags of my mp3-collection.
PVAStrumento and
Cuttermaran to cut my TV-recordings.
Camstudio for recording screen-vids.
DVBViewer to watch TV.
VLC-Player for most of my videos.
Mediaplayer Classic for ogm-Files (VLC doesn't handle them that well).
Type: Programming
APIViewer 2004 to find values of constants.
DebugView for debug-output.
OllyDbg for debugging-purposes (foreign applications).
HxD as hexeditor for RAM and Files.
PSPad for AHK-Programming and other file-types-editing.
Winmerge to merge files.
Type: Management
TotalCommander for FTP and other file-managment.
FoxitReader for PDF-Viewing.
Kompozer for HTML-Editing.
Type: Others
Chainsaw to split files in smaller pieces. Does provide a batch-file to reassamble the file without any software installed.
Trillian for ICQ, MSN, IRC.
FastStoneCapture for screenshots (I've version 5.3. which was freeware, it's now shareware).
MWSnap as alternative.
And many many more. Some are german-only. For the others I was too lazy
Thalon