I went to the Frosting the other day and it's a really cute little store. The lady who works there is super-sweet and helpful. They've got all sizes of boxes as well as cardboard trays to put the cakes on in the box - decorative and plain. You can rent decorative pans, and there are a ton of plastic decorations to choose from.
Pros: Wide selection, super-friendly staff
Cons: Hours are a little less convenient