Get the CORSAIR Vengeance 4GB (2 x 2GB) 240-Pin DDR3 SDRAM DDR3 1600 Desktop Memory Model CMZ4GX3M2A1600C8 for $27.99 (after MIR).
The price you pay up front is $57.99 and the mail in rebate is for $30. I have sent in rebates to corsair in the past with no problem. I receive them within a fairly reasonable amount of time for mail in rebates. The rebate offer ends on May 5th.