Personally, I think the simplest effects are the best. The ultimate mentalism trick is to get someone to think of anything, a word, a picture, a song, whatever, and then tell them what they're thinking of. I see most mind-reading effects as an approximation of this, maybe with a kicker at the end, or with a more convoluted plot, but essentially that's what's going on.
Therefore, my favourite mentalism effects are a book test and a card force. As long as you frame them in the right way they can be absolutely mind-blowing, because they genuinely appear to be an act of pulling information out of their brain. PM me if you want me to run through my handling and presentation of these effects.