You can download VMWare Server 2 for free and it comes with a web interface to create/manage virtual machines. I ideally wanted something similar to Microsoft System Centre Virtual Machine Manager to manage multiple hosts. Unfortunately you have to pay for both VMWare and Microsoft’s offering (but SCVMM is free on our MSDN subscription).
To manage a single host, without using the slow/buggy web interface you can use the free vSphere management app that comes with the free version of ESXi. You need to download and copy a directory to your install dir of vSphere, which is available here.
Full instructions are available at Andrea Benini’s blog at linux.com.