4GB Kit 2 X 2GB DDR2 Memory for Dell Optiplex 755 760 GX280 Ultra Small Form Factor Desktop PC2-6400 240 pin 800MHz Non-ECC DIMM RAM (PARTS-QUICK Brand) at Amazon.com
Dell Optiplex 755 Desktop Core 2 Quad (Q6600) Ram
8GB 4x2GB PC2-6400U DDR2 800mhz RAM For Dell OptiPlex 755 760 960 XPS 410 420 AB | eBay
i found this dell optiplex 755 in a scrap yard perfectly functioning{came with side panel just have it off} its ungodly slow with only a single stick of ddr2 2gb ram and
8GB 4X2GB Dell OptiPlex 755 Series Desktop/PC DDR2 PC2-5300 RAM Memory at Amazon.com
Dell Optiplex 755 SFF Intel Core 2 DUO 3.16GHz 2GB RAM 160GB HDD Desktop PC | RecycledGoods.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