SFF, so mini-itx?
I used a Silverstone SG06.. (though with the 300 watt sfx power supply) to build my mom's mini. She likes it, and it's nice that it doesn't take up a ton of space. Any GPU installed will have fairly nice ventilation from the fairly open side perforations, although I might tinker with the fannage if i were going to install a high power gpu.http://www.newegg.com/Product/Product.aspx?Item=N82E16811163172
That one has the upgraded PSU.. be sure to choose it, rather than the older variant, for a gaming machine, if you plan to utilize a modern gpu.
Be warned that most slim optical drives, will utilize a micro sata connector cluster. You'll need a converter to connect it.
Be sure to do some research on the available power connectors from the psu as well. Believe the 300 watt psu has 1 pci-e connector, iirc.