wheretogo.com seems to figure a lot on Webfeet also.

Webfeet has got to be the best starting point (after http://cresby.com of course)
Because Martin is proactive in collecting info and has a huge database of bands/venues. Indeed the only times it goes wrong are bands that are actually doing a concert or source info is wrong.

Ceilidh organisers - there is a thread here about a ne Yahoo discussion group.