There are only a handful of companies that are currently producing a connection broker product.  If you dig through the documentation from HP, IBM, and others they mention this “optional” magical box that serves as the bridge between the client devices and the hypervisors.  Very few of these vendors who are pushing VDI have come forward and presented a solid connection broker component, which I would consider to be one of the most critical components of VDI.  I have listed them here for convenience in evaluating end-to-end VDI solutions.

ChipPC Virtual Desktop Center
http://www.chippc.com/management/xcalibur-global/index.asp?p=Overview
ChipPC makes a full computer that fits into a wall socket, while that may be an interesting concept, I have doubts about their ability to work with VMware, Microsoft, and others on creating a solid connection broker product.

Citrix Desktop Broker -> Citrix Desktop Server -> Citrix XenDesktop
http://www.citrix.com/xendesktop
Citrix has what seems to be all of the pieces needed to produce a connection broker product that is head and shoulders above the competition.  They have a very efficient transport protocol (ICA), they have a solid delivery platform (Web Interface, Secure Gateway, Access Gateway), they have figured out load balancing, session management, and the list goes on and on.  However, they have not yet made their connection broker product, which has now undergone two name changes,  utilize all of their existing technologies.  It still remains to be seen what the new release of the XenDesktop product will bring, although after much hype at the recent iForum 2007, the technical preview of the XenDesktop product has been pushed back to the ambiguous “early November.”  There has also been some feuding lately between Citrix and VMware after the recent purchase of XenSource by Citrix which also rasises concerns about the future compatibility of a Citrix connection broker package with VMware or other manufacturer hypervisors.

Dunes Virtual Desktop Orchestrator (VD-O)
http://www.dunes.ch
Dunes Technologies was recently acquired by VMware, which I can only assume means that VMware wants to incorporate the Dunes VDI product suite into their own product lineup.  A quick glance around the existing Dunes website reveals that the Desktop Orchestrator (VD-O) product is missing.  Because of this I don’t know that Dunes or its once upon a time VD-Oproduct

LeoStream Virtual Desktop Connection Broker
http://www.leostream.com/productVHDC.html
Currently the LeoStream product only supports the VMware hypervisor.  While this may not be a problem for existing VMware environments it does pose a problem should an alternative hypervisor emerge as a better platform for VDI.  In terms of feature set and scalability the LeoStream product does seem to be one of the current market leaders.  IBM is also referencing the LeoStream product for their VDI architecture.

Propero workspace
http://www.propero.com
Propero was acquired by VMware in April 2007, and the Propero website now redirectes to a VMware page that doesn’t give much insight into what they plan to do with the acquired Propero technology.

Provision Networks Virtual Access Suite (VAS)
http://www.provisionnetworks.com/solutions/vas/vas.aspx
Provision Networks seems to be one of the only independent (not associated with a hypervisor technology) connection broker manufacturers that really understands what people want in a connection broker.  They support nearly every hypervisor on the market, they have a web interface, they even support the logical pooling of a mixture of virtual and physical machines.  The one thing that I did find alarming was the frequent mention of a Provision Networks VAS client.  This would mean that existing terminals, computers, and other end points that may already have RDP or even ICA clients would need yet another remote connectivity client.

Zeus Virtual Desktop Connection Broker (ZXTM VDB)
http://www.zeus.com/news/press_articles/070423-001.html
Zeus already being a player in the web server, load balancing, and traffic management markets seemed to be a good fit for entering the VDI connection brokering space.  However other than a several month old press release there is no information about the ZXTM VDB product on their website.  Have they discontinued the product?  Will the technology be incorporated into one of the other ZXTM product lines?  Until there is some more information it is hard to consider them a player in the connection broker market.

In summary if you are evaluating VDI and need a connection broker solution the only two choices available today are the ones from LeoStream and Provision.  Technically the 1.0 version of the Citrix Desktop Server is also available but it is lacking in its feature set and will likely be discontinued in favor of their new XenDesktop product.
If you can afford to wait then it will probably be worth it to see how Citrix improves upon their XenDesktop product and also what VMware decides to do with their recently acquired technologies.