The Green Note Jazz Jam
This happens on Sundays fortnightly (that's twice a month) I went once...dressed in a pink shirt, beret, cravat and elegant scarf. I looked the part and everyone definitely thought I was cool.. anyway, the quality of the jam was good.
Not particularly well run; you just hopped up when you felt like it and blasted a tune. I remember the pianist playing one chord in first position the entire time during our rendition of Mr P.C. which made it sound naff...depends on who's there.
I also had to sit through 2 hours of the house band...while good the night was billed as a jam session.
The Blues Kitchen
I used to live just down the road from these guys, and went there more for the fine selection of whiskies and rather attractive bar-staff than the actual music. However they do run a couple of jam nights - Sunday's from 6pm.
Its a blues jam. So unless you can put up with 4 hours of 12-bar blues and pentatonic/blues scale abuse avoid!
The quality of the blues was actually OK as blues goes. But for a cynical blues-hating old man like me...
The jam itself is very well run, with an announcer and clip-board and everything.
A side note: I've just noticed that swing patrol teach there Monday's. I went to a few of their lessons a while back which were tons of fun, full of beautiful women and easy to join in on. Plus Scott is a good bloke so go along if you fancy learning some scintillating dance moves. http://www.swingpatrol.co.uk/
The Jazz Café
Don't let the name fool you. Jazz does not occur here. They sold out and have no souls.
The UCLU Jazz Jam
While not technically in Camden its close enough. This is every Tuesday during term time on the 3rd floor bar (Phineas) of the UCL Union building from 8pm.
Its mostly populated by students at UCL from the jazz society. There is a wide mix of skills there and its very much a free-for-all. Worth going to, if not just for the gorgeous students and cheap booze.