Not specific bands but many sites the came up after the fall of mp3.com:
www.hxcmp3.com
a great resource for people to experience hardcore music. Though an aquired taste, some may find it interesting
www.soundclick.com
another great resource, much like hxcmp3, many bands, signed or not, can join and post their music for download. Contains many different genres. My band Hyline has a few songs avaliable for download here.
www.purevolume.com
same as the two above but also have many signed bands for download as well.