This is a link to several hundred muds. It's a great site, check it out.

The Crypt is a pretty good mud that I've recently discovered. I highly suggest at least taking a look at it.

Waterdeep is the "sister" mud to The Crypt (or is it the other way around?). It's pretty good, I suggest you try it as well.

Avatar is the first mud I ever heroed on (I'm a Lord there now). It's extremely newbie friendly, although the "family environment" of it gets extremely...STIFLING after a while. Still, it is pretty fun.