I've compiled a list of the main apps/utilities I use and recommend. I see multiple posts in the forums from new owners asking what monitoring app to use, etc. This list should cover all of the basics.
1. HWMonitor - a small app used to monitor CPU/GPU temps.
2. Auslogic's Disk Defrag - a very fast alternative to Vista's own Disk Defrag
3. GPU-Z - a lightweight utility which can be used to check clock speeds of your GPUs.
4. CPU-Z - another handy utility from the makers of HWMonitor, this little app will display info on your current CPU clocks/multiplier along with info on installed RAM, etc.
5. CCleaner - of all the registry cleaning tools I have tested, CCleaner is the safest and most effective of the bunch. This one I use almost daily to ensure the registry is free of old/non-essential entries. It can also be used to quickly access and enable/disable startup items.
6. Recuva - another top app from the makers of CCleaner, this utility can be used to restore files that have been accidentally deleted from your computer, memory cards, mp3 players, etc. If you've ever accidentally deleted an image from a camera memory card and needed to recover it, this is the app to have installed.
7. ExtractNow - is a great compliment to Vista's built-in .zip archive support. I use this one for all the .rar files I encounter. It supports the following formats: ZIP, RAR, ISO, BIN, IMG, IMA, IMZ, 7Z, ACE, JAR, GZ, LZH, LHA, TAR and SIT. I leave .zip archives to Vista, but the others are handled by ExtractNow.
8. Notepad++ - This is one of the best freeware source code editors I have ever used. This little app is essential when it comes to modding INF files and other formats. It also features a very handy built-in 'Compare' feature.
9. Stardock's LogonStudio Vista - this cool app is a lot of fun. You can take any .jpeg file and turn it into a Vista Logon screen. Take a look, this app is great. Did I mention the app does not have to be running in the background? Launch it, set your Logon Screen and hit apply. That's it.
There you have it - my recommended freeware app list. If I think of any others I'll update the list.