I am using the NZXT Gamma case, and larger heatsinks keep me from mounting fans at the top of my case. I would like a heatsink or fan that is small enough to let me mount fans and let me keep my overclocked CPU cool. It is more difficult to determine the size of heatsinks when shopping online.
To better help you, What h/s fan are you useing now? Is it stock? What is the most you are wanting to spend on a good h/s & fan that will fit? Because you can put in a Corsair H70 for just under $100 (or an H50 used for about $50) that will help your OCed cpu and leave you plenty of room to add your fans. I have the H50 on a 965BE overclocked to 4+ghz on a daily rig and it works GREAT for me.
I'm using Thermaltake Black Widow, I'd like to pay less than 100 dollars. I'll check out the H50 though
I would have to agree with paco and would say to go for the Corsair h50/70. I have an h50 on a Athlon II X4 620 clocked to 3.65 GHZ idles at 29-34c and tops out at 48C running occt or prime95 for 2 hours plus, while running games it's usually around 42C.