gfxCardStatus is a menu bar application for OS X that allows users of late 2008 — 2011 MacBook Pros (15″ and 17″) to view which GPU is in use at a glance, and switch between them on-demand.

Switching to the integrated graphics card seems to drastically cool down my current MacBook Pro. The battery life also gets better. I’ll simply always switch the graphics card if the MacBook isn’t plugged-in (can be done automatically) or I work with it on my lap while it’s still plugged-in.
Great, so I’ll probably don’t have to buy the new one. Thanks to Kim for the tip.