Resistor value depends on the LED, voltage, and current. You can use this page to calculate:
One thing to note is that if you're absolutely certain your pulses will be fast enough (typically 0.1 MS or faster) you can overdrive many LEDs. For example a bunch of SMD LEDs I used in a recent project normally run at 20 mA but for short pulses can be driven up to 120 mA. The upshot is they're almost (but not quite) as bright when being strobed in a matrix as they would be when run standalone.
Chris