I love my Apple Magic Trackpad, but it can be tricky to get working on a Windows machine, so I decided instead to try out the Logitech T650 Wireless Rechargeable Touchpad. So far so good. The feel is very similar to the Apple trackpad, and the gestures (even under Windows 7) are tweakable so they feel more at home.
For instance, if you go into Logitech Mouse and Keyboard Settings application, you can adjust the two-finger scroll to behave like OS X’s tracking of your finger movement, effectively inverting the scroll (though the settings doesn’t word it that way…).
They can be had at Amazon for under $40, and to have more of a Mac-like experience on a Windows machine, I think it’s worth it.