I agree that VirtualBox would be good for you if you don't use VMs for "extracurricular" uses. While VirtualBox is good for some stuff (programming, Office, Web browsing, etc.), if you plan to use USB devices and/or game with your VM, I would suggest going with one of the commercial solutions (I prefer Fusion). Being Open-Source, VirtualBox doesn't have any DirectX support or USB "IDing". Example being if you plug in a USB printer and want to use it in your VirtualBox VM, there is a very good chance it will not work. Sames goes for USB Controllers or anything above a USB Mass Storage Device. Know this from personal experience.
If you just need something simple, VirtualBox is a good, free alternative. If you want/need better hardware/software support in your VMs, I would go with Fusion or Parallels.
