Logical people need to be involved in an effect for it to mean anything to them. Mental magic or tricks that borrow their objects or tricks that take place in their hands can all help to dispel the ideas of you employing magical props of any kind. Next minimize your show of skill. The last thing these folks deserve is an easy out like -- "Boy you have fast hands!"
Instead, let the magic happen in their hands or heads and use reverse logic to take preemptive strikes to eliminate any explanation these folks may have latter on when they try to reconstruct the routine. Take them down the garden path and turn the hose on 'em. They'll love you for it, because you have now forced them to recognize the possibility of improbable.
In short, items need to be examinable, borrowed and/or given away. These people will keep any reminder of this type of effect as evidence of this impossible event. Their memories will allow them to exaggerate what you did if only to help explain the fact that they were completely fooled. I hate the word fool, fooler or fooled to be used to describe anything I consider magical; however, these analytical types will want to minimize your efforts. Their egos are less threatened by using such disparaging remarks or references to your work -- so words like trick, fooled or puzzle may help them deal with this dilemma.
Listed below are some tricks that I feel fit these requirements, but these are just a few. They are also my opinions and you'll have to form you own opinions of the magic you perform to these audiences. I hope this helps.
-- Signed Card to Wallet (or Jay Sankey's "Paper Clipped" if you can't afford a nice wallet)
-- Michael Ammar's "Shadow Coins" (Easy to Master Coin Magic tapes/DVDs) or David Roth's Coins Across (it uses the same gimmick)
-- One-Hundred Dollar Bill Switch
-- Jay Sankey's "In a Flash" (Great trick that's easy to do)
-- Signed Bill in Lemon