I recently discovered the Wish Special Events blog, and it is a wonderful resource, especially for weddings around the DC area. They have everything from venue reviews to tips on the cheapest place to rent chairs, to, most recently, info on secret (at least from me) ribbon outlets! Purr. I want to take a trip to buy ribbon now. Unfortunately, I probably need to do something about my current (excessive) ribbon stash first.
My other favorite ribbon source? The J. Crew outlet in Lynchburg, VA. One weekend each month (pretty much), they have an even bigger sale (as in, shoes in the catalogue are $200, in the outlet are $70, and at the outlet sale are $7) that's held in the actual warehouse, and it's a mad house! But there are also amazing deals to be had, and they actually sell their ribbon (like, the ribbon used for belts or flip flops). It's in giant bolts (at least for ribbon), and it's way cheap! I love it! But... this is part of the reason that I now have way too much ribbon.