I've got a few additions to make on top of my original entry.
Media:
PowerISO: I've had several uses for this as of late, the biggest being to burn CDs in MP3 format (saves a lot of space for more files, if you didn't know). It also gives you the ability to set up virtual drives, as well as extract files from ISOs. (Oddly, I can do the latter with WinRAR of all things as well.)
K-Lite Codec Pack: Good lord, this is useful. This allows even Windows Media Player to play a relatively-wide range of files, all the way from MP4 to M4V to even MOV. This extends to every other media application, even Movie Maker. No more downloading extra programs to be able to do what you want with a single video.
Handbrake: Video encoder. I sometimes use this in conjunction with Fraps to encode the massive video files it puts out, as well as to convert a video to a different file type (often times WMV or AVI to MP4). It can also rip movies and the like from DVDs, but I haven't tried this before.
Other:
SpeedFan: Allows you to monitor hardware readings, such as fan speed (
it does exactly what it says on the tin), CPU usage, and hardware temperatures. Handy for old computers, or computers with bad thermal paste.
Paint.NET: Photo editor that falls somewhere between MS Paint and Photoshop. Feels a lot like GIMP. I do a lot of my pic editing in the standard Windows 7 Paint (sue me), but when I need to do something a bit more advanced - say, edit a picture while saving transparency - this is what I use.