SugarSync
The beauty of SugarSync is that much of the work is done behind the scenes on the SugarSync servers, which eliminates bulky software downloads. You sign up for the service and download a very small application, install it, and you're ready to go. The program will walk you through.
SugarSync also offers a completely free 2GB storage option, which includes all of the great features of the SugarSync service but is totally free, no credit card trials, no strings attached.