later in the spring im planning to have a body paint party, and for the clothing that people do wear its like dress up/neon acid style clothing. something you might see in an MGMT music video. don't have a good name for it yet.. stoked tho.
Jagermeister party - everyone brings a bottle of Jager and wear flannel or hunting gear.
Dress as your heritage - I'm mostly german so I could wear a beer maid outfit... if I was russian, i'ld bust out a sweet fur hat.. and so forth.
during the tour de france my buddies threw this huge party called the tour de booze. we set up teams and events (pong, funnels, shotguns, strikeout, dizzybat, flipcup, card games etc...) and everyone dressed up in biker gear.
In all seriousness, the trick is to pick something that people will actually do. I would love to go to a robots and hoebots party but no one is willing to dress up like that. One time we did Jersey Night...everyone wore like a sports team jersey and that was super fun. I think a halloween party around this time of year would be fun.