Syncing files from multiple Macs?

Is there a simple script or app to make sure folders and their contents on 2 Macs are always syncronized with the most up-to-date versions? I'd use my .Mac account but my files are too large to keep uploading and downloading to my iDisk. Both Macs have Airport Extreme so I'd love to just have the 2 machines talking directly to each other. Any solutions?

Thanks!