I bought 2 sets of (4x2GB) RAM from MemoryAmerica.com back in 2008 and 2009 for my Mac Pro.
It cost a fraction of the Apple cost ($250 instead of $800 each set) and lifetime warranty fitted as standard.
Since then I have had 2 bad RAM sticks, 1 in each of the sets. MemoryAmerica couldn't have been more helpful.
They sent me out a whole new set of 4 (2 matched pairs) each time for RMA and only charged me shipping on them.