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RemoteBuddy works very well. I use it to control one older G4 Mac mini which is functioning as a media center in the study. Has a remote function, a remote keyboard and even a remote screen function as well as a ton of other features.
 
Snatch lets you pinch and pull to resize windows

And Snatch has 10(?) customizable buttons that can be assigned to keyboard shortcuts. Also, multi-touch is used as TheZimm posted but also two fingers scrolls a page up and down. There is also a keyboard that works instantaneously, as with the trackpad function. Snatch is definitely the best on the App Store, but it is only for Mac. If you primarily use a Mac, GET IT!!!
 
WiFi Touchpad - another option

though there is not yet mac support, we are assured it will come out in early 2009, so here is a glimpse at yet another option: WiFi Touchpad
 
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