Look at the forums on the Footstompin list (www.footstompin.com), this is a regular question there.

Sandy Bells (Scottish on Sunday afternoons and Wednesday nights, Irish most other nights) and the Tass (Scottish most nights) are always worth a try, but there are several others with a session one night a week, and others that have regular guest singers or bands. The Royal Oak is a pub that acts as a regular (very small) concert venue. And Edinburgh Folk Club meets in a concert venue that feels like a pub.

You don't need to restrict yourself to the centre, the bus service is good enough to get you back from events even as far out as Musselburgh, Balerno or Penicuik.

For something really different, try the storytelling night (last Friday of the month) upstairs at the Waverley Bar ("The Guid Crack Club").

I'll be away for part of September (I'm a regular at Sandy Bells on Sundays, sporadically at other sessions).