No costume venture is complete without a trip to Display & Costume. I think they have a rental department, but they mostly cater to people like me who enjoy cobbling together their own costumes from various parts. They most recently saved my butt this past New Year's Eve by carrying fake Uzis. (I attended a James Bond-themed party.) The toy guns looked real enough that only minor modifications had to be made. Best of all, the Uzis have an awesome rat-a-tat sound effect. (NOTE: Toys R Us and other toy stores do not carry any guns other than Nerf or "ray gun"-type guns anymore because kids apparently get shot up by cops that think they are carrying real guns. Also, there's some issue with morals and teaching kids that guns are bad or something like that...)
Display & Costume is definitely a one-stop shop and prices reflect that. Some things are cheap (fake Uzis) and others are not (fabric). They have a section in the back where you can buy fabric and assorted ribbons and other fabric novelties. Mostly, the store is a haven of accessories for almost any costume you can dream up. They also carry party supplies, including more unusual items like fake palm trees for your luau-themed parties. At Christmas, they have a whole room of elaborate Christmas decorations. Perhaps best of all, the store is located near the Northgate Mall, Pacific Fabrics, and Target, so you can always stop in at those other stores if you don't find everything you need!