Mmm, I guess there's been a lot of stuff over the years, but if I had to choose one type of under-appreciated postage, that would be my fanmixes, particularly the Solidarity fanmix (Kyler/Creed) (http://noorie.livejournal.com/53114.html) and Time of Storms: an unofficial soundtrack (Snape/Lupin) (http://noorie.livejournal.com/136700.html), but also the Wesley fanmix (http://community.livejournal.com/jossverse_radio/667.html) and teen!emo!snupin (http://noorie.livejournal.com/127282.html).
Oh, and one PSA post that I'm linking because it might also be useful for your, er, comm: PSA: How (not) to report download-related errors (http://noorie.livejournal.com/132042.html)
Speaking of which, check this out! (http://www.stereogum.com/archives/004735.html)