Gucci-Mamma
For the light itself, I would start with what color you'd like your LED's to come in.  I went with green for this project.  You can get 'em in several colors: red, blue-green, aqua, pink, violet, ultra-violet, white, orange, amber, yellow, and blue.  You can also get blinking, tri-colored, or blinking tri-color, too.  Bloooo is a hot color these days, being invented only recently (1993, and big props to Shuji-san who lost his patent), and they're used for producing the white LED's, among others colors.  I'd say, get the brightest ones you can find in your color of choice.  Which, LED's have come a very long way in terms of brightness.  LED's are measured in milli-candela, or mcd's, and the brightest ones are around 10,000 to 20,000mcd's, which is nowhere near milli.  You can do some serious damage to your eyes with these.

Anything with a warning label gets my attention!

So, I kinda splurged.  I took a little trip to the Geeks Paradise that is Fry's Electronics.  Fry's is a mixed bag.  I scored and found pack of 100 resistors in the value I needed (75 Ohm) for $1.50, and some pretty ferocious 10 candela green LED's.  These are actually Nichia LED's, NSPG500S's, rated at 12 candelas each.  I bought 6.  At $4 each.  Mega-ouch.  I also had to root through the packages to find 6 that hadn't been broken into and stolen.  I kid you not.

Bring the pain!

Shop for the cheapest-ass USB cable you can find.  USB cables are unbelievably overpriced, and besides the color there isn't much difference between the $4 no-name to the $20 Belkin cables.  There is even less difference between them when you chop them into little bits!  I found a box full of 15-foot A-A USB cables (freaks of nature, and shouldn't exist) at a flea market for $4.50 each.  I bought three, realizing that I can chop them in half and make six strips of LED's.  Score!  I also found a 45CFM Delta fan for $5 at the same flea market.  Double score!

Now that we've got all the parts, it's math time.  Run for the hills!  Okay, so the LED's I got are 3.6V, 20mA devices.  USB uses 5V, so we need to shed 1.4V to power them properly.  From there we use Ohm's Law to figure out what kind of resistor we need to use.  Anyone got the answer yet?

A little algebra, solve for R. Convert milli-amps into amps.  Do the math.  Crunch, crunch.

R=V/I -> R=(5.0-3.6) / (.02) -> R=(1.4) / (.02) -> R=70 Ohms

I used 75 Ohm resistors, which is close enough.