Sound editing
Let me first start by making the following disclaimer: I know absolutely nothing about sound editing. However, I happened to find myself in a situation recently in which I had a fairly distorted and echo-y recording of one of my dissertation interviews, making transcription an absolute bear. After messing with the settings in Windows Media Player, I finally came up with the bright idea to check online for some simple (and cheap!) sound mixing software. I found Audacity, a free, open-source editing tool that has a decent UI (as these things go) and lots of great one-click filters that managed to salvage an almost unusable and hissy recording.
Yay for open source!