More than you want to know about lamination...
In hot lamination, you put the thing to be laminated in a plastic pouch, then run it through the laminator -- just hot rollers, really -- and the heat seals the plastic together. This gives the best results.
There's also cold lamination, where the item is essentially stuck between two layers of adhesive-backed plastic. In a cold-lamination machine, rollers are used to apply pressure to the pouch. You can also buy "self-laminating" sets, in which the front side is hinged and you stick it down by hand. These are mainly sold for ID cards, but bigger sizes are available if you go to the right suppliers.
Playing-card size isn't standard, so if you're having your cards laminated at a print shop (or buying a laminator to use at home) you'll probably have to use the next size up -- maybe photo size -- and trim off the excess.
EDIT: Phooey, I took too long to write this and others jumped in! At any rate,
here's one place that seems to have a wide selection of self-lamination stuff.