As people are adding some free downloads heres something from a good netlabel, a compilation with some great names from the more experimental end of the spectrum. http://escalared.com/archives/651 The escala netlabel releases are always worth investigating. http://escalared.com/
Also the Clinical Archives netlabel, which released Magical Unicellular Music in the past and now seems to focus specifically on free improv bands. http://www.clinicalarchives.spyw.com/