I have come across a number of threads in the past that talks about 1,000s of Scuttle, Pligg, and PHPDug sites that you can use to build links. By the time you get to them, most of them now have expired domains, they've removed registration, submissions are broken, or they have removed the software completely. Suddenly those 1,000s of sites become a couple hundred. I've compiled a list of close to 400 that have been active over the last month. If you find this at all useful, let me know.