I blathered on a bit about VMWare a while back, and lots of people recommended VirtualBox. I'm trying VirtualBox 3.1.2 with Windows 7 host and Linux guest, and it works surprisingly well. I've used it successfully to hack on a bunch of projects while I'm stuck on a Windows laptop (shudder).
Installing was essentially self-explanatory. I never read any docs, except when it came to installing those "Guest Addition" programs to allow better mouse-handling. And I had to look up how to go about sharing folders between host and guest. But the documentation was clear, I found a short description how to set up the share and then and a command to run to mount the host folder:
sudo mount -t vboxsf ShareName /mnt/mountpoint
I'm using Gnome in my guest, because I haven't used it in a long time and I was curious what'd changed. I'm amazed even Compiz works in the guest. I recall a time in the very recent past when my computer couldn't even handle Compiz natively, let alone in a virtual machine.
Perhaps the best part about VirtualBox compared to VMWare is that there is one product called "VirtualBox" and one download link that took me a matter of seconds to find. Fancy the thought.