Patriot PSD34G13332S Signature 4GB PC3-10600 DDR3 Notebook Memory for $18.99 shipped after this $7 rebate.  Here is a screenshot for your reference.  This notebook memory features PC3-10600 (1333MHz) data rate and non-ECC unbuffered 204-Pin 2 rank double-sided in-line memory module..  Most places have it for about $25.