What's a wearable project without LEDs? Designed specifically for wearables, these updated Flora NeoPixels have ultra-cool technology: these ultra-bright LEDs have a constant-current driver cooked right into the LED package! The pixels are chainable - so you only need 1 pin/wire to control as many LEDs as you like. They're easy to sew, and the chainable design means no crossed threads.
So, you want lots and lots of NeoPixels? And you want them for less? Not a problem! Here's a sheet of Flora NeoPixels fresh from the (reflow) oven. Snap them off as you need 'em and save a pretty penny while you're at it. Each order comes with 20 pixels on a snap-apart sheet.
These pixels have full 24-bit colour ability with PWM taken care of by the controller chip. Since the LED is so bright, you need less current/power to get the effects you want. The driver is constant current so it's OK if your battery power changes or fluctuates a little.
Each pixel draws as much as 60mA (all three RGB LEDs on for full brightness white). In theory, the Lilypad can drive up to 500 pixels at 30 FPS (it will run out of RAM after that). However, after about 10 pixels (or if the distance between pixels is more than an inch or two) the resistance of the thread can affect the power supply. For large quantities of pixels over 10, you may want to consider using stranded core wire or copper braid to provide a "power bus" for the pixels - the current draw will add up fast!