MillionaireNextDoor: Radio Shack carries blue LED's but like Supradude noted, they aren't at all stores. (I hit 6 different locations in the San Fernando Valley before I found them.) Radio Shack part number 276-311.
Zaku: I have the blue LED's in an Enlight 7327 case. My mobo is a KT7 Non-RAID. LED specs: 5mm, 5 volt, 30mA, 300mcd.