If you want a gangsta themed routine grab an Ellusionist video on "Street Magic" as they call it for the effects and for patter just memorize a rap CD

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Personally, I'd stick with money effects, card effects, and "pain" effects (i.e. needle through arm) because to me, that is what describes "street life". When it comes to money effects, I think greed is the right way to go, also sh4de, and anything else that you can think of that involves visual, quick, to-the-point money magic. Also some color changes with cards along with some quick, high-impact card tricks (an ACR routine perhaps?). And lastly I'd do some "pain" effects, for instance, disjointed, needle through arm, candle through arm, etc...
For patter, do what you normally do- they might want a gangster theme, but they still want you to be doing magic and not some "gangster punk".
Hope that was somewhat helpful,
~David R.