Open Trackers.Org a blog that posts when private trackers are open for registration. There will not be as many listings as some of the others here, but these are usually hard to get into sites.
Media Torrents another forum thread with open site listings posted.
Invite Paradise has listings of open trackers in this forum. There is some other helpful information at the site, but you should not need to pay or donate to get anything useful.
Have had a few inquiries lately about private sites, so I decided to put up a short guide.
Advantages of private sites:
1. Privacy-only registered members are active on a torrent.
2. Content is almost always clean and real.
3. Speeds are generally better
4. Some cater to specific interests
1. Maintaining proper ratio can be difficult.
2. Power hungry administrators can be a pain.
The requirement of a proper ratio generally insures excellent speeds as users remain active on torrents longer.
Additionally, many members of private site use seedboxes which provide excellent upload speeds.
However, this also has its issues as it may be difficult to maintain a proper ratio with so many active seeds on a torrent and this results in being unable to download new material. For newer users, I suggest sites that give credit for keeping a seeding torrent active (without uploading).
On the vast majority of private sites knowledge of the content you are downloading is restricted to members.
Generally speaking you should be able to run your bittorrent client 24/7 to have success with private sites.
This post primarily is about getting in to private sites.
Most private sites are invitation only, which means an invitation from an existing member is the only way to get in.
On occasion, these private sites do open their membership up for others.
As of December 16, 2013, I have added new links and all links are working.
There are several sites that monitor private sites for open membership.
BTRACS is my favorite place for checking. Most important is their distinguishing those trackers that are rarely open from those that are generally open. Also, they provide the Alexa ratings for the sites. They update their information every ten minutes and I have found their information to be reliable. Sites may be sorted alphabetically, by category, language or Alexa ranking. There is no RSS feed. They also have a Forum for Open Signups.
OpenTrackers.net monitors private sites for openings. Does not differentiate between always open and rarely open sites, but has a pretty comprehensive listing. You can see trackers that have recently opened (or closed) on the right hand side. A little difficult to navigate around, but still a very good source.
Zeropaid Open Trackers Sign UP Thread a forum thread listing open signup private sites. You should go to the last page of this thread. If you register there, then you can "watch" the thread for updates and receive email notifications.
Torrent Invites.Org another thread of private trackers that are open for registration.
Torrent Invitez forum for posting of private sites open for registration. Not as well populated as the others here.
I hope those of you looking to get in to the world of private trackers found this post informative and helpful.