The fairly incredible indie netlabel Deep Elm Records has a ton of samplers available for free download. There is something for everyone here – from postrock to punk, it all rocks hard. I started with the sampler Postrockology, and I’m working my way through the rest. It’s a mixed bag, and some of the tracks are better than others (there are a few that I just don’t care for at all, but only because if style and substance – everything I’ve heard so far is technically excellent). Definitely go here, check things out. I’m sure you’ll be kept busy for quite some time.