FileList.org about 5 or 6 years ago, followed closely by bitsoup.
Had only those two for ages.
Lost both my original accounts tho when I went traveling.
demonoid. Although my first truly private was bitme.org. And through that site alone, I got into bitmetv and waffles where they were both extremely hard to get in to.
I joined MySpleen in 2006, and still have my account. Probably joined Kraytracker before that, but my account ended up being pruned. I joined Demonoid in July 2006, even though it's not what I considered private.