I was thinking that a thread specifically for outlines of different jam structures would be very helpful. I'm sure everyone has times when ideas don't seem to come to them, and something like this would help.
I'll go first with 2 chord kind of thing:
Jam in 7/4, split in 4/4 and 3/4--except it alternates the order:
A7 / / / Dm#7 / / Aadd6 / / Dm#6 / / /
The chords are based off of an A Mixolydian with the addition of a chromatic flatted 6th (D minor has f natural, but Aadd6 has f#): A B C# D E F F# G A.
The idea isn't only restricted to chord progressions either, i.e. motif based jamming, etc.