Our graffiti party was apparently pretty good, although I wasn't actually there (road trippin' to a football game). Really though, it seems to me that the best parties are when there isn't a big discrepency between the number of guys to girls, or that the party is so big that there are still plenty of people of the opposite sex to go talk to. I know that as a freshmen we often complain that there are never enough freshmen at events. So I would reccomend first of all try to get a lot of house participation.
Other themes that have worked well this year-- $5 Prom--everyone got some really trashy, ugly formal gear for this one--again I missed this one being DD.
A Masquerade Ball- that was pretty cool, formal attire, date party, make sure everyone gets masks. I would reccomend these stipulations however. 1) No mask no entrance 2) you must keep your mask on at all times (trying to keep your identity a secret was part of the original fun of old masquerade balls, however I do realize that this will be hard w/ drunken greeks.) 3)Try to get everyone to show at the same time--explain the rules, like you must keep your mask on and whatever else you might want to make up.
Gnarley Harley party--was pretty decent as well (but I was sick, WTF is up with me missing good parties???

) Lots of leather, and tattoos.
Those have been the best theme parties we've had--our hicks n' chicks was poorly attended by the brothers, partly b/c another sorority that we are a quite a bit closer with was having a party that same night, so most of us ended up going to that which was a hawaiian them.
Basically if you have good attendance then everyone is going to have a better time--and while date parties are a good thing, the best parties aren't date parties b/c then no one is worrying about impressing someone from the start. Also--at least for us date parties are BYOB which always causes a struggle for the underage. Plus it's kinda awkward asking a girl you may not know very well (like whether she drinks or not) if she wants something, b/c if she doesn't and she's a GDI you come off sounding like an alcoholic greek. <steps down from mini soap box> sorry about that, i'm a little stressed right now, and moody, i just need to rant about something.