Two I've made recently are:

ABC's
features songs from three different artists that start with A, three different that start with B, and likewise for C.

The artists included were:
Alfie
The Arcade Fire
Autour De Lucie
Blonde Redhead
Boss Hog
Bright Eyes
Cash Audio
Cub Country
Cursive

Another comp. I made was "Waking Up." I included serene songs to wake up in the morning to.

I Really Should've Gone Out Last Night by The Dirty Three
Duck Pond by The Sixth Great Lake
Another Train by Ian McCulloch
Painted by Eamonn Vitt
Port Sunlight by Birdie
Volcano by Damien Rice
My Little Corner Of The World by Yo La Tengo
Open Ocean Sailing by The Radar Brothers
Hiding Behind the Moon by Jeff Hanson
Porchlight by Kingsbury Manx
If Everything Fell Quiet by The Reindeer Section