Many Indie labels and bands provide around 2 songs of each release as a 128kbps MP3. Just take a look at
Saddle Creek (Bright Eyes, The Faint, Cursive, Desaparecidos),
Epitaph (too many to list -> Punkrock/Hardcore/Indie) or
Barsuk Records (Death Cab for Cutie, The Long Winters, Kind of Like Spitting, Nada Surf, Rilo Kiley). Others utilize MP3.com, which I personally don't like, since it requires you to give an e-mail adress each time you download.
Last but not least Punkrock label
Go-Kart Records has made several of their recent complete releases available as 192kbps MP3s
here.
Even if you don't like Punkrock/Hardcore I'd advise you to read their letter to the RIAA.