Went here the other day to get some last minute items for a murder mystery party which I procrastinated putting my costume together. I ended up finding what I needed, but there is a large selection of costumes here. I just wished that the prices really reflected what the costumes are worth. A lot of the materials are pretty flimsy... yes, you only need them for one night, but man it can get expensive depending on what you are going for.
Other than the costumes, there is a wide selection of party items... from different themes to just color plates, etc. I think they even have wedding stuff, but you won't find me in that section any time soon. ;)