Have an Android phone? This virtual mouse and scroll wheel is mint.

www.Gpads.mobi has a great virtual mouse program.
It is by far the easiest program of this type i have ever dealt with, aslo the most customizable.
you can customize it for keynote, itunes, frontrow, ect. The best thing about it to me is that it functions like the trackpad on my macbook pro.
Two finger scrolling is great. It's just a great tool if you use your computer as a media hub, now the phone is your remote.
so yeah, It's good.

*UPDATE* 9.29.2010

I find myself using this touch pad more than a real mouse! It's so comfortable and easy too. My wrists are less strained, along with my elbows, they aren't bent all the time now, its easy to extend you arms and just watch the screen. I really recommend this app, I'm buying the full version ASAP!