To clarify, the DIL package is the style of the ATMEGA chip on your Arduino and the SO package is the style of the USB driver chip.
For your LEDs look at www.ledshoppe.com. They have white LEDs, a package of 100 for $10 including shipping, and if you sign up for the newsletter, they'll even through in a keychain laser pointer/flashlight.
I've bought from them and they seem to have good customer service as well as good products.