4GB 2X2GB RAM Memory for Lenovo ThinkPad X Series X60 ( Type 1706 ) Black Diamond Memory Module DDR2 SO-DIMM 200pin PC2-4200 533MHz Upgrade System Specific Memory - Newegg.com
X61, still a great writing/ second machine after all these years : r/ thinkpad
2GB Memory RAM Upgrade for the Lenovo Thinkpad R61 Series, T60 Series, T61 Series, X60 Series and X61 Series Laptops (DDR2-667, PC2-5300, SODIMM) at Amazon.com
RAM memory for Lenovo ThinkPad X61
OFFTEK 2GB Replacement Memory RAM Upgrade for IBM-Lenovo ThinkPad X61 (7762-xxx) (DDR2-5300) Laptop Memory at Amazon.com