I use paste wax. There are products specifically for this purpose sold at most woodworking tool stores, but I've never tried them.
A spray lube I've been using a lot lately is "Dupont Teflon Multi-Use", sold at Lowe's. I haven't tried it on my saw top, but it should work well for that purpose. Really good stuff; it quickly dries and leaves a waxy coating that holds up well.