Where does everyone buy decorating supplies online? Trying to find reasonable prices for Sprinkles, etc...

amazon.com and Global Sugar Art.  But the best way to get a good price on cake supplies is if you have a coupon for a store like ACMoore or Michaels.  They are somewhat limited to Wilton products and Duff products, but for sprinkles and basic needs at an affordable price they are good.

If you don't mind spending more for better quality, Global Sugar Art has good stuff.

If you have a tax ID, then you should look into CK products.  They have good bulk pricing.

Enjoy!