VMWare Player vs Workstation

The main difference is that VMWare Player can run, but not create virtual Machines. Workstation can do both.

Update: It appears versions > 3.0 now include the capability to create Virtual Machines, but as stated by hawkdsh, it still lacks some of the advanced features such as snapshots.

You may also want to check out VMWare Server which is also free.

More information on all of them here.

No longer true. VMWare Player can create new virtual machines, but lacks the advanced features of Workstation, such as snapshot capability and integration with the VMWare enterprise products.