Musicalimprovcomedy.co.uk is Heather Urquhart and Joe Samuel's blog about musical improv. They feature podcasts in which son strcutures as well as all kinds of genres are demoed. They also provide training tracks. Further material contains interviews with various improvisers specializing in musical improv.
Site has invaluable material for anyone interested in musical improv.
Joe and Heather are based in Brighton, UK and perform with a local troupe named The Maydays.