SSD gives new 21.5-inch iMac signifcant speed boost | Macworld
Internal SSD DIY Kit for Apple 21.5-Inch iMac 2011
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