Are you referring to the FOLDED card to mouth or just placing a card in yer mouth while they are not looking? There is a pdf book I know about that talks about the folded card in mouth (Grin) as well as many videos. Simon Lovell for one.
Mac King has a nice card to shoe that was printed up in a Genii magazine a few years back. There is also JB magic's Shoe't which is a nice idea. For card to impossible place I recommend Carl Cloutier's Card to Sock.
Card to impossible place is always a crowd pleaser.. even if the magician isn't.
You can find a GREAT card to shoe in the New York Magic Symposium DVD. The effect is by Lisa Menna and is currently the method I use. It can be found here: http://www.elmwoodmagic.com/?nd=full&key=4646
Ah, well there it can become a bit trickier, at least if you want it signed. The folded card to mouth and shoe and such are usually just the easiest ways...cards are easier to palm when they are folded. However if you don't want to use a signed card, I would recommend just learning a good force and plant a duplicate somewhere else, or at least that is how I might do it but I usually use a folded card to wherever signed if I am going to do this kind of transposition.
Something even simpler you might think about would be a card to pocket.
David Stone's Real Secrets of Close Up Magic DVD teaches a nice version of the card to mouth. However, the DVD is full of other tricks and effects, and, as a result, is a bit more expansive than just a single card-to-mouth effect.
there is a card to mouth in the DVD inside magic on the Ellusionist site. Its not that hard to master. Its the best one i have seen for people just starting out