Seems the same question's already been asked on SuperUser - Where can I find Ubuntu Desktop releases on a vmdk
The following is the accepted answer:
I have not found any official ubuntu website distributing vmdk's.
According to http://www.vmware.com/appliances/directory/
very few suppliers of ubuntu desktop on vmdk exist (3 to be exact).
This seems to be focused on vm creation and distribution, and for now
I consider this the de-facto website to go to for ubuntu desktop
These guys seem to have vm creation and distribution as a side-project
to their main line of business: http://www.quotrader.com/
but the highest-voted answer is as follows:
You can find many VMs on VMware's site.
Open the site and go to "Virtual Appliances"; Ubuntu LTS 11.4 is one
of the many images there.
The newest Ubuntu 11.04 VMware appliance starts out of the box with a
desktop looking like Gnome 2.x, but can be transformed to start the
Unity desktop from Ubuntu. Contrary to the basic Ubuntu 11.04 image
this one has the latest VMware Tools installed.
Note: The VMware's site also seems to have Ubuntu 12.04, both desktop and server versions but it's the VMWare store and you have to buy it.
The OP also adds:
just make sure you have installed the latest vmware player so you
don't have problems like I had with vmplayer not being able to run an
virtual image made with a newer version.