When you do a Youtube search for Keith Johnstone, the top video is on trance mask work and the column to the right has several other short videos that offer some colourful blips:

(Will Weigler (willweigler@YAHOO.COM)

If you are looking for information related to improvisation in the context
of improvisational comedy (though much of this material overlaps to other
theatrical contexts), there are some webpages with histories of 10+ years on
the internet. The pages range in terms of quality; many of them are linked
together, so you can keep finding similar threads.
Some examples include: (this has been the longtime centre of improv on the
web, but it appears to be down now - maybe permanently?)
Prominent US groups (with some resources): (NYC - Tina Fey, etc) (Chicago creators of longform, with a base in LA as
well) (Chicago - the 'rebels' of the longform
scene. Mick Napier's Improvise: Scene from the Inside Out is a wonderful
text) (San Fran)
Prominent Cdn groups (a sampling):
Impatient, Bad Dog, Instant Theatre, Crumbs, Catch 23, PROJECT Project,
Ghost Jail, National Theatre of the World, Second City.
There's also Improv Everywhere, but they fit into a different category
(flash mobs, public performance, etc).

(Nicholas Hanson
Associate Professor
University of Lethbridge,
Department of Theatre & Dramatic Arts