Try something like 220Ω. I usually run LEDs straight off the microcontroller pin, no resistor, but thats for visible colors. IR is around 1.7 volts, might be a little much. I/O pins are limited to 20 mA, which is the same as most LEDs...
Anyway, the IR LED will show up white in the viewfinder on your camera. Works better in a dimly lit room, not real bright when lit directly, and less bright if pulsed. Some cameras filter IR more strongly than others, but you should still notice some difference.