You guys listed all the good ones, except the 4-disc Lost Legends of Surf Guitar, which is just amazing. Also, I really like "Experimental Japanese Music", this weird Japanese album with GRound Zero and a Takashii Miike interview in the middle of the whole thing. Also check out "Classical Chinese Music Played on Traditional Instruments". I did a comp a few years ago for xdiedenroutey called "Just Because your Music Wears Thin doesn't mean You're In Shape" which had new songs from Darth Vegas, Cock ESP, Point Line Plane, Violetta Beuaregarde, Warmth, Scissor Shock, Haunted Castle, Yellow Swans, and a ton more... here's a link to this Adam Cooley-curated comp tracklisting (which I have no copies of): http://www.discogs.com/release/650313 ... Also, Neon Matte Dream of an Octafish, an excellent Beefheart tribute comp.

hell yeah!!! probably my favorite punk comp ever.

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nothing short of total war
the old school black metal comp. fenriz curated is pretty ace.

This is another superb one:

CHINA – the sonic avant-garde
POST 005 2xCD digipak

This first-ever, 2-hour survey of the current experimental music and sound art scene in Mainland China features 15 artists mostly in their twenties from all over the country. The double-CD set shows what is really happening today on the Chinese new music cutting-edge. No more symphonies or string quartets with self-Orientalizing titles and pentatonic motifs. In fact, you won't hear one Chinese instrument here. The incredibly wide range of styles cover everything from plunderphonics, musique concrete, experimental electronics, ambient, sample collage, plug-in modulation, text-sound, sound poetry, mixer feedback improv, hardcore noise, radio art, political satire, to post-concrete recording art documenting a family karaoke scene. This is only the beginning of something unpredictable. No to be missed.

All three Nuggets Box Sets (Rhino really outdid themselves with the tracklisting on these)
Rockin Bones (Another fantastic Rhino box)
No thanks (yet again, another fantastic set from Rhino, this time its punk)
Sub Pop 200

Two old favourites. I second that Nuggets one as well.

A lolt of great ones but, this one is essential: