There's a national open mike listing,
generously maintained by Paul
Roub. He's on the record as agreeing
WUMB maintains a list of upcoming folk events and venues.
The folks at townonline.com maintain a wonderful, informative
about coffeehouse activity in eastern Massachusetts.
The folks at Shenandoah Music have constructed a nationwide list
of open mikes.
And here's one from the Bay Area: http://www.bayareaopenmics.com/.
I began listing open mikes on my Web site in March 1998. Since then, a
whole pile have come and gone. Here, I list the open mikes which have
been reported to me as being no more (sleeping with the fishes,
etc.). I'll be listing these alphabetically, with the date of first
listing and the date I reported them as deceased (before July 1999,
it's the first date they were removed). These dates are approximate,
since I'm always a little behind.