Mouse Jiggle ftw
http://mousejiggler.codeplex.com/
I use this in IT when having to be logged into several machines at once, and not have to re-enter my admin password after 5 minutes of activity over and over and over again. (To bypass any security, run it off a flash drive)
A free solution.
I work from home a bit also, as do my colleagues, we all use this.
This software requires no installation (so good if you have restrictions on your laptop), and can be run off a USB key. Keeps my session unlocked all day.