It depends on what you're looking for, Alex. Check bit torrent sites first, because you'll get the file faster that way. If you're looking for older and/or less popular files, try eMule ,(
http://www.emule-project.org for the free installer). It's easy to use, and it usually has 4-5 million users, depending on whether it's a weekend, (more users), or a weekday.
It helps to be very specifis with the words used in the search parameters on this one. If your request is too vague, the results you're looking for may not be displayed, but a more specific request would display the files you're looking for. eMule is open source, and they come up with new versions every few months, but it's not necessary to be using the most recent version.