CMS 8GB (2X4GB) DDR2 6400 800MHZ Non ECC SODIMM Memory Ram Upgrade Compatible with IBM Lenovo® Thinkpad X61 Notebook Ddr2 Pc6400 Sodimm - A41 at Amazon.com
4GB 2X2GB Memory RAM for Lenovo ThinkPad X Series X61 (7674ES7) 200pin 667MHz PC2-5300 DDR2 SO-DIMM Black Diamond Memory Module Upgrade System Specific Memory - Newegg.com
2GB RAM Memory for Lenovo ThinkPad X61 7678 Black Diamond Memory Module DDR2 SO-DIMM 200pin PC2-5300 667MHz Upgrade System Specific Memory - Newegg.com