Flexx DIY Bundle with Transcend 230S SSD to swap main HDD for SSD on all 2011 iMac
Amazon.com: OWC SSD Upgrade Kit for 2011 21.5-inch iMacs, Mercury Electra 250GB 6G SSD, 18" SATA III 6Gbps Data Cable, Installation Tools and iMac Screen Adhesive Tape Set : Electronics
iFixit Offers Kit To Install 2nd Hard Drive in Mid-2011 iMacs - MacRumors
OWC DIY Drive Upgrade/Install Kits for Apple iMac Models
OWC DIY Drive Upgrade/Install Kits for Apple iMac Models
Internal SSD DIY Kit for Apple 21.5-Inch iMac 2011