I use limewire and bearshare. I've tried torrent and morpheus, but went back to lime and bear. Limewire doesn't have any popups, but with bearshare, you have to accept that "SAVE!" crap to download onto your computer as well. Whats a few popups, when your getting music and stuff for free?
I've noticed that if I can't find something on limewire, I usually can w/bearshare. Also, with limewire, I usually can't watch any avi. files, but with bearshare I can. But with limewire, the "preview" will always work, but with bearshare the "preview" hardly ever does. So if I'm downloading something to watch, I can check it to see if its what it says it is with limewire, but I have to wait until its finished downloading with bearshare.
I got alot of Ali G from the British shows on Bearshare, along with alot of other cool stuff unavailable anywhere else. Its great for seeing NHB fights from different shows like Pride and UFC, and underground fights.
But both limewire and bearshare claim to have better versions if you upgrade to their "pro" versions for about $18 apiece, but I haven't tried any of those yet.