RAM for late 2008 Macbook?
From EveryMac :

RAM-Type = PC3-8500-DDR3 SDRAM @ 1066 Mhz

Supports officially max. 4GB and unofficially max. 6GB, 
but indeed a total of 8GB on ROM Version MB51.007D.B03 
and if running Mac OS X 10.6 or higher.

Apple released an update (including 8GB support) here.
Also check for information about it here.

And if you are unsure, which to buy: here are some on amazon.co.uk