Monster mash

"Raiding the 20th century" was DJ Food's hour-long exploration of the late 20th century (mostly all about the origins of modern popular music, via tracks that themselves sample other sources). This is archived at UPenn and worth listening to several times.
DJ Food: Raiding the 20th Century (Words & Music Expansion)
There is also an earlier, rawer, 39 minute version that went out on XFM in 2004, but its legality is even more dubious.
Strictly Kev: Raiding the 20th Century - A History of The Cutup (tracklisting and more info)

I'm personally rather partial to several of the mashups referred to in the mix, and it would be nice if one could buy them!

The Raiding mix is quite strange, because of the limitation on only using mashups, bootlegs, cut-ups, and cut-ins as source material. While I agree that mashups are a valid and important form (and that in some sense much art is of this form), I disagree with Strictly Kev's apparent contention that it is likely to become the dominant form. That is, unless one uses a very broad interpretation of "mashup".

I do agree with him that the Kylie Minogue live (but possibly mimed?) performance at the Brit Awards 2002 was one of the sublime peaks of pop music, and a great mashup. But I also think Cat Power's performance of Wonderwall is sublime, and this is pretty far from a mashup unless one includes it in the category because of its structural elements or because it is a cover.
Kylie Minogue: Can't get Blue Monday out of my head (live)
Cat Power: Wonderwall

Here Minogue, whose output is in my opinion generally fairly lacklustre, performs a generic pop song to the backing of a great piece of music, and does so in a way that perfectly captures the mood of the times. (Given the date of this performance, I'm thinking Nero fiddling here...) On the other hand, Marshall takes a piece of music performed by a band I do not like in a way that is irritating and self-conscious, and shows just how great the song can be with a dose of focus and honesty.

I've found that there are many noteworthy snippets in the Raiding mix, and that it repays repeated listening. I especially recommend The Tape-Beatles and Steinski, who both crop up several times, and The Grey Album.

Many Tape-Beatles tracks are available for free download from UbuWeb. I love the track Stress from Music with Sound.

Three wonderful mashups of Beatles tracks are squirrelled away at Steinski's web site. Some of his best known work is also now available to buy as the "What Does It All Mean?" retrospective. Presumably these have now been cleared, or at least someone is prepared to absorb the potential flak.

The Grey Album is now de facto official, as the record companies appear to be leaving it alone. It probably helps that it may have significantly boosted the sales of both The Black Album and The White Album.