Ubuntu – Creating & running Windows virtual machines

What's the recommended way to run virtualised Windows environment on top of Ubuntu nowadays?

I need to create new Windows virtual machines too, not only use existing ones, so, to my understanding, VMware Player would not be enough.

I've used VMware Server earlier, but I'm having too many problems getting its latest version to work on latest Ubuntu (11.04)… Probably related to this:

VMware has declared VMware Server End
Of Availability on January 2010 with
the actual support ending on June
30th, 2011. […] Furthermore, VMware Server is
not officially supported on Ubuntu
releases greater than 8.04.

So, are there any good alternatives to VMware Server?