If you are concerned with the temperatures and want to reduce them elevation of the rear of the machine helps, as sitting flat on the desk only reflects the head back to the base of teh Mac. You can buy passive aluminium coolers like Rain Designs Mstand or iLap. Most powered coolers are designed for PC notebooks and dont work overly well with Mac`s one cooler that does work efficiently is the Moshi Zefyr 2, as it`s principle of cooling is specifically designed for Apple portables, by blowing the air across the base of the computer.
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Moshi Zefyr 2
You can use software to manually override Apple`s own cooling algorithm by manually taking control of fan RPM and setting up power profile presets with SMC Fan Control (needs update for 2012, temp sensor presently not recognised), or you can look at UltraFan which allows you stipulate a preset temperature and the software will automatically raise and lower fan RPM`s to keep the system at the predefined temp.