Intensive tasks, such as gaming, video editing and consuming Flash Content will always generate intense heat in your MacBook. One can go so far by following the advice above, but if you need to preform intensive tasks and there is no way around it the CPU and GPU will get taxed, which will cause heat - The reason desktop computers don't have as many overheating problems as laptops is because they disperse the heat better by being larger, having better cooling systems and having more ventilation. And believe-it-or-not, you can equip your MacBook with a better cooling system!
Laptop cooling pads are devices that one places either in-between their laptop and their lap or their laptop and a desk. Modern laptop cooling pads use advanced airflow-controlling techniques and extra fans to effectively cool down laptops. They protect you from the heat of your computer while cooling it down to ensure it a long life. Laptop cooling pads can be very cost effective, starting at literally a few dollars, with the more high end models still very affordable at about 30 USD. Below are a range of cooling pads that MacInfo recommends because of their high efficiency and user satisfaction rates when used with MacBooks:
Note: When buying be sure to select the link (USA or UK) that corresponds with your country -- as you cannot buy a cooling pad from the Amazon USA site if you live in the UK, and vice versa. If you live in neither the USA or the UK you cannot make a purchase, unfortunately.