We don't usually post sample compilations around here, but I think this particular one is worth it. Spinalonga Records is a Greek label and A Sampler Darkly is a free offering of 16 tracks from various underground Greek bands, hovering around the post-rock, electro-rock and alternative areas. These compilations are a great way to discover new bands you like and I've found some really cool stuff here. My favorite cuts from this are This Is Nowhere, Psychedelic Trips to Death, One Leg Mary, Their Methlab, De Sades and 45Rats, but I like pretty much every track on this compilation. Also, it's a lot of instrumental stuff, so it's really good study music.
You can check out the Spinalonga Records Bandcamp Page for more free compilations - they have more heavy stuff in there, too, and I bet there are some really cool bands waiting to be discovered.