Since my genre of choice is dance music, I use Soulseek, which I think has done a great job of carrying Napster's torch.

The trouble is that many of the tracks I'm into come from the personal collections of assorted DJs or diggers on Youtube, so obscure tracks are often in poor quality: I've had to resort to using Discogs to purchase the original vinyls and recording them through a sound card. I am not yet a pro at digitally cleaning up some of the minute crackling that occurs, and buying a brush to clean the records hasn't helped much...