Patrick Rouse created a great VDI Connection broker comparison. Patrick works for Quest/Provision Networks, but he serious investigated the VMware VDM and Citrix XenDesktop solution. I know that some people reviewed this matrix just to be sure that this document is as accurate as possible.
This connection broker comparison matrix compares Citrix XenDesktop, VMware Virtual Desktop Manager and Provision Networks Virtual Access Suite.
It's a nice starting point in investigating which connection broker fits your needs. BTW: What are you connection broker needs?!
The broker comparison can be downloaded here: http://blogs.inside.quest.com/provision/files/2008/05/brokercomparison.pdf
Interested in VDI, maybe this article can help you: https://www.virtuall.nl/articles/PublishedArticles/LanVisionVDIenglish.pdf