8GB (4GBx2) Team High Performance Memory RAM Upgrade For Dell OptiPlex 755 Series (Desktop Mini-Tower and Small Form Factor). The Memory Kit comes with Life Time Warranty. at Amazon.com
OFFTEK 2GB Replacement Memory RAM Upgrade for Dell OptiPlex 755 Series (Desktop Mini-Tower and Small Form Factor) (DDR2-6400 - Non-ECC) Desktop Memory at Amazon.com
8GB 4X2GB Dell OptiPlex 755 Series Desktop/PC DDR2 PC2-5300 RAM Memory at Amazon.com