This is what I've been using. I could go without the pointy laser front end but besides that this thing is phenominal. Batteries last a LONG time, no connection issues like the targus handheld presentation trackball and it has a trigger left click for clicking and moving a map, VERY useful.
It can be found here
http://www.iogear.com/main.php?loc=product&Item=GME321R
Troy