These are the ones I currently use:

http://www.tlavideo.com/
http://www.moviemountain.com/
http://www.redlightvideo.com/
http://dirtybirdpictures.com/

These sites have affiliate programs as well. RAD has never gotten back to me after submitting their online application and currently their site is down. Citiboyz is going through some changes with their site and affiliate stuff.

http://www.citiboyz.com/

I'm sure there are plenty more out there as well.
Where would you go to buy videos online? Go there and sign up. Even amazon has an affiliate program.