I've posted before on Excavated Shellac, a site dedicated to '78 rpm recordings of folkloric and vernacular music from around the world'.
But there are many more shellac/vinyl archaeologists out there. One of the most interesting sites I've come across recently (thanks to Bob from Brockley) is Locust Street, whose author seems to have set themselves the task of telling the history of popular music in the twentieth century year by year - starting with 1900, and now reaching as far as 1909. As well as music, there's lots of historical material and some great contemporary images.
Also of interest is Snap, Crackle and Pop, rediscovering 'The dusty sound of old records, other people's detritus picked up from boot sales, flea markets and charity shops. Forgotten music for our enjoyment'.
I just wish I had the time to listen to all this music... though careful what you wish for - plenty of people are finding themselves with more time on their hands at the minute, but without the money to enjoy it: it's called mass unemployment.