Firstly make sure when your using the laptop not of the vents are being blocked. This can often happen when resting a laptop in your lap and your clothing blocks some of the ventilation causing very rapid heat build up.
Secondly, as mentioned above, get yourself a can of compressed air and attempt to clear out some of the dust.
Thirdly, after-market cooling options are available. These consist of flat platform with built in fans that you rest the laptop on and the blow cold air onto the base of your laptop keeping the whole unit cooler.
There are many variations, but this picture shows the general idea behind it. http://b4tea.com/wp-content/uploads/2010/05/cooler-for-laptop.jpg