These are all very old links. I'll put some more usefull ones here someday...
MP3's
The MProgg3 page has Mp3's of some of the most popular Swedish "progg" bands of the 70's like Nationalteatern and Nynningen. Notice however, these bands were mostly politically progressive following the tradition of singer/songwriters like Bob Dylan and Leonard Cohen, as opposed to the musically progressive bands like King Crimson. As I grew up with this music I still enjoy it very much. I must say though, Nynningen had a lot of Mahavishnu in them and would probably be appreciated by many prog fans if they only re-released some of their other albums. These samples are from their first album and are mostly "blues-rock". The Nationalteatern/Nynningen song "Doing the omoralisk schlagerfestival" is a must have though!
The Prog Rock Listening Booth has new Mp3's every week of prog bands from all over the world you probably never heard of. The guy has a love for Italian prog which I'm not very fond of, but I've found some wonderful stuff here that has actually made me go out and buy the CDs.
The Punk Rock Mp3 Web Ring Punk Mp3's are not very hard to find, and the good thing is the bands really shouldn't give a shit, that's anarchy for you! :) If you're looking for something, this is probably the place to start. I'm not very fond of the 90's punk bands, but I've found some old classics here like Crass, Dead Kennedys etc.
Soundfonts
If you're into soundfonts you've probably been to these
places already, but just in case you've missed them,
here are some great resources for soundfonts:
Samples
www.mellotron.com The official Mellotron site has tons of Mp3's of the sounds available for the Mellotron/Chamberlain. Every file features 3 notes, convert them to wav files, edit them a bit, and they're perfect for using with your sampler/sound card. Also of value if you're interested in the instrument and want to hear the sounds you probably never heard before like the woodwinds, guitars, vibes etc.
SampleNet Tons of free samples here!