Here're some open trackers that I add to every new torrent file I download. They're pretty useful, since most of the time they help me get the number of peers up for some of the rare ones.
Most modern torrent clients would let you add new trackers. You just need to add the following lines:
udp://tracker.publicbt.com:80/announce
udp://tracker.openbittorrent.com:80/announce
udp://tracker.openbittorrent.com:80
See below for more info and a list of more trackers.
References