Without sounding patronising (or repeating yet
another suggestion for the Ambitious Card

), I'd suggest visual, fast paced, high impact effects which can be done in the hands; either yours or theirs. Remember, your hardest challenge in this situation is holding their attention and it helps if there is always something happening or about to happen. For that reason, flourishy type routines would probably come accross well.
You could always go down the Blaine route and make an effect out of a simple DL and duplicate card. Infact, his material would be the best source for inspiration on this sort of thing; particularly his first two TV specials which are found on the DVD Mystifier.
Ellusionist.com also pander to the masses by providing specific "street magic" effects, as does Penguin.com and a few other online retailers.
Other than that, and seeing as I have very minimal experience in actual Hit and Run Street magic, I'd aggree with the above suggestions.