This is the best place EVER! Yes costumes are available year round but I find myself coming here a lot more for party favors and decorations. This where I came for the Bachelorette party favors (damn, that was a good party), came here for wristbands for a few of the house parties, really awesome deal for their balloon bouquets. Wedding, baby shower, birthdays, office parties, even just the good' ol kickback at the crib, this is the place to go.
Let me just say this, if you find yourself pulling your hair out at one of the more popular, commercialized party supply stores, take yourself down there to Sahara/Jones, right on the side of the Fiat dealership and take a gander. I promise, I find myself buying stuff I don't even need sometimes.
Holiday decorations, they have that as well but, it's not like Christmas THREW UP all over the store. This is a YEAR-ROUND/ALL SEASON type of store. Really, go check them out, it's rare that I leave disappointed.