what a tiny case you have !!! well, i think you might take one off these http://www.newegg.com/Product/Product.aspx?Item=N82E16835118030
ZALMAN ! nice one, the best you can get with the space you have i think.
SIZE: 120(L) X 123(W) X 67(H)mmhttp://www.newegg.com/Product/Product.aspx?Item=N82E16835106068
or this baby thermaltake cooler, seems nice, have good reviews
Fan Dimensions 80 x 80 x 20mm
Heatsink Dimensions 90.2 x 84.3 x 39.0mm
The zalman is a bit tall, by 10mm, and way larger by 40mm
Its up to you !