if in the usa you can pick up a pair of ath-m50's on ebay open box but new for $99 with free shipping. in terms of audio quality they are great for that price. closed design with a small soundstage so not generally bought for gaming though they will work. excellent for everything else. they do have a bassy sound signature.
if you definitely wanted open cans for the soundstage for gaming and a little bass but not bassy sound then the hd558 run about $110 and should fit the role great.
if you are more of a budget shopper the creative aurvana live! mentioned earlier is a good choice for the money however i think the hd558 or m50 are a bit nicer if you have the cash.
the ad700x mentioned is about $110 as well and is great for...