I think it's more than fair to also mention one commercial affiliate solution, which supports VirtueMart+Joomla!: VM
Affiliate . It's is a complete affiliate solution designed specifically for
VirtueMart and Joomla! It is J!1.5 native, and VM 1.1 compatible, yet
supports any older version.
It is completely built upon the VM and Joomla! framework, easy installation via a Joomla!-like installer.
It's nicely integrated into the site's frontend, and also uses VirtueMart's administration style in the backend.
Due to its integration in VirtueMart, many tasks that are done manually in ordinary affiliate software, become automatic in VMA, such as commission approval/removal and so on.
VM Affiliate is easy to use, but yet very powerful - making affiliate marketing a much more simple job for any VM shop owner.
You should give VM Affiliate a try.