There is one more option, Sun VirtualBox.. and CrossOver if you prefer.
So you can pick any
- Boot Camp. Included with Mac OS X 10.5 (on intel Macs) - free, but you can use either Mac OS X or Windows at any time, not both
- VMware Fusion. $ 79, can use an existing Boot Camp partition. If you use any other VMware Product (including but not limited to ACE, Workstation, VirtualCenter, ESX, Lab Manager, View Manager, VDM ...) the VMware vm format is cross compatible. You can also try for 30 days before buying
http://www.vmware.com/download/fusion
- Parallels. Priced like its competitor (above), and was the coolest Mac OS X virtualization product before Fusion came out. But comparing these two will create fuss so give it a try yourself (again 30 days trial) to see which one you like more
http://www.parallels.com/ also can use an existing Boot Camp partition
- VirtualBox
http://www.virtualbox.org/wiki/Downloads free, but can't do anything 64-bit etc etc (which is still a limitation of also Parallels if they didn't update their code with last release?)
- Crossover for Mac
http://www.codeweavers.com/products/cxmac/ $ 39 and the main difference is that you would be running basically individual applications, not virtuallizing the whole OS