CMS 512MB (1X512MB) DDR1 2100 266MHZ ECC Registered DIMM Memory Ram Upgrade Compatible with Cisco® 2811 Router Main Memory DMemory Ram Upgrade2811-512D for Server Only - C89 at Amazon.com
Amazon.com: MEM-2900-2GB= 2GB DRAM Memory for Cisco Router 2921 (PARTS-QUICK ® BRAND) : Electronics
MEM2600XM-64D 64MB DRAM Memory for Cisco Router 2600XM Series (PARTS-QUICK Brand) at Amazon.com