NICAR-L is a busy list (expect 10-20 messages a day) hosted by the National Institute for Computer-Assisted Reporting.
It's frequented by hundreds of working journalists whose CAR skills range from expert to beginner. To join the list, send this one-line message: SUB NICAR-L firstname lastname to listproc@lists.missouri.edu.
JAGIS-L: Tom Johnson's JAGIS homepage is at http://online.sfsu.edu/~jagis/. There's a sign-up link there.
CENSUS-L was started early this year as an offshoot of NICAR-L. Discussion is primarily about the Census, but there may be talk about mapping as well.
To join, send this one-line message: SUB CENSUS-L to majordomo@nicar.org