Forgotten Isle
One of the most interesting talkers I have encountered, Forgotten Isle is a Telnet talker (using SiNCO 0.8a by Stile - a FI user). The basic idea is of being stranded on an island with only the other users for company.
Besides the usual chatter and scenery (which is quite good *IMHO*) there are several pretty cool functions and events. An ongoing storyboard - sometimes in the Mountains or the Forest - allows everyone to contribute short segments to see how a story evolves with the co-operation of many people with different styles and ideas, occasionally users are auctioned off to one another for purposes unknown *grin* and (an idea of which I am quite fond) there is a nerf arena...
If you have a Telnet client, you can telnet directly to Forgotten Isle at forgottenisle.net port:7020.
The administration structure is quite extensive which means that there is almost always someone (Wizards, Archmages, Mentors, Advisors, and Admins) there to help you out if you have a question or a problem.
If your web browser supports Java, you can log in to FI without using Telnet. Just go to
http://forgottenisle.net/classes/forgotten.html
and wait for a while for the application to load.
One of the only problems I have encountered in my time as a FI user is that due to time differences, (combined with the scarcity of FI users from this part of the world) I am sometimes stranded all alone... Oh well those are the vagaries of cast away existance!