Throwing this out here in case anyone is interested. I've started uploading screencaps of various costumes for reference on Photobucket. They're just from Hulu+, so they're only 720p, but it's better than nothing.
(I can get okay caps if a character stands still for a second or two, but Hulu seems to like using some pretty gnarly compression when characters are moving around a lot).
Stills/promo shots and unsorted images are in the main folder. Sub-albums of screencaps on the right listed by episode. It's a small selection so far, but I'm going to start trying to get caps of some of the costumes I like and add them. If anyone has suggestions for additional costumes to add, let me know.