I have had a few successful JV's with some pretty big names in IM.
I was basically creating different products and services for a niche group of people that were all members of a particular IMer's program. I was marekting them pretty passively and through word of mouth. Pretty soon the program owner took notice and came to me asking if I wanted to JV with him.
Granted I had to weight the difference between giving up a cut of the profits with the fact that I would get access to his entire list and therefore a much broader slice of the niche pie.
Well I made the leap and went for it. That one JV alone now nets between $8,000 - $10,000 a month in sales.
I have basically repeated that process now a few times with other program owners as well.

I am now in development of a program of my own in a completely different niche and will be launching in November.