I"ve been having great success with Soulseek! I've been able to find a bevy of rare (or at least obscure) files in the experimental, ambient, electronic, and post-rock genres, and I've even searched for pop stuff and found tons of returns. Connecting has never been a problem, queueing is not nearly as bad a Winmx, although I've only been able to download one file at a time from each user.
Maybe it's time to give it another shot--Nir seems to have handled the AG onslaught pretty well.
www.soulseek.org