Do you have a motherboard already? Or is this a new build?
There's a variety of miniITX cases, depending on preference, which might suit your needs.
I own a Bitfenix Prodigy which is pretty small and can fit everything really, but it's footprint isn't really a lot smaller than a standard tower, it's just smaller overall.
I'm also a big fan of these two cases-http://www.silverstonetek.com/product.php?pid=333&area=enhttp://www.silverstonetek.com/product.php?pid=291&area=en
ITX and mATX versions of the same case. Both can fit a GTX680, though the ITX version needs a slightly awkward PSU.