My two favorite mental effects that I first ran across in Genii:
The Color Out Of Space (February, 1989): The performer shows 4 envelopes, each with an ESP symbol. While the performer's back is turned, the spectator chooses one of the symbols/envelopes, opens the envelope, removes the pen and notepad inside, duplicates the symbol, then hides the drawing in a pocket, and places the envelopes out of the performer's view. Without any questions, the performer is able to divine the chosen symbol.
Hummeracle (March, 1990): Bob Hummer's 3-card trick, well routined by Max Abrams.