One of the newest printing techniques available to me now is called "Spot Varnish". Basically, after a card is printed on a full color off-set press, it passes through the press one more time to "print" a coating of glossy varnish. Usually, this is done as a solid coating because it adds waterproofing and a nice glossy look to cards. Some printers (like mine) offer an option to print specific parts of the card with the varnish.
I really like using this technique because it can add a little something special to any printed card. Here is an example of an invitation I just finished:
Since more than 900 invitations were being sent, the client needed to keep the costs down but still wanted a formal feel to the invitation. I thought a tone-on-tone pattern added to the border would do just that, so I printed the card with a plain black border and added the spot varnish as a pattern only on the border. I carried out the same technique on the reply postcard for consistency.
Another way I've used the technique is to call out an aspect of the invitation in a subtle but sophisticated way. This Bat Mitzvah invitation has each event card called out not only by it's distinct color, but by writing "celebration" or "bat mitzvah" in a spot varnish. Cool, huh?