Brian, you should state your approximate location - country will do. Assuming you are in the UK (from the names you mentioned), here's a first cut:

Spiers & Boden
Dan McKinnon (Canadian, but tours the UK every year)
Duncan McFarlane (a 'Catter)
Marilyn Middleton
Hilary Spencer & Grant Baynham

You are right about clubs booking from the same subset of artists all the time. But if a club is democratic enough to listen to its members' wishes, and if those members get about a little bit, (festivals, other clubs etc), then some outside influence seeps in. We are particularly lucky at Herga and St Albans to have a number of gigging artist members and other members who frequent festivals, and we get our new ideas that way.

It helps not to have too strict a price policy too. If you are only looking for acts up to £100-120, you are self-limiting to your immediate vicinity or the up-and-coming ones (i.e. you don't have quality guarantee).

But the best answer is - get out and about, go to festivals, and take your pick. There are a lot of good acts out there.