@cosinekitty
In circuits like this, where you are driving a bunch of LEDs as a unit, I have found that you don't need a dedicated resistor for each LED.
Yep, I know it looks tempting to just use one resistor for all the LEDs.
One resistor works great, but if the voltage drop of each leds is significantly different, some won't light, or will hog more current; when one burns out or goes 'open' then the others take up its unused current.
I saw someone do this only last week with a dozen expensive blue leds, that were slowly dying like they had some kind of virus!
This has particularly comical effects on a breadboard, when you decide one led isn't working, and try to replace it...
@dumptyhumpty
That's good I can get that stuff at Radio Shack
Sorry, I was kidding about RS: you should try to avoid them at all costs! Try a local store instead of corporate if you can, it's almost always a lot cheaper... my local supllier will sell me 100 1% resitors for $1 CAD, whereas Radio Shack want $2 for five. Suport small business if you can-- it's the Arduino way!
Would it be ok to use these prewired LEDs?
thise are 12V leds, with integral resistors.. you would neeed a separate 12V power supply for them, but sure they'll work. You could power the Arduino from the same 12V supply. For something expensive like super-bright led's, you might want to try Digikey.