Folk London is excellent, and commendable for having online listings as well as the printed version.

I use the Peterborough Folk Diary quite a lot - I'm on the mailing list and I know it is actively maintained. Martin Nail's site is a good starting point for English music all over the country.

Google searches often help with finding sites (try "folk " plus a day of the week and a county for instant tour-planning info!). There's no single resource that gets it all, and many (including some listed above) are out of date or link to sites that are out of date.

Anahata