How-To: Now's the right time to swap your old iMac's hard drive for a fast new SSD - 9to5Mac
27" iMac (Mid 2011) Optical Drive Installation Video - YouTube
Amazon.com: 2nd 2.5'' SATA HDD SSD Hard Drive Disk DVD CD ROM Optical SuperDrive Caddy Tray Adapter for Apple Unibody MacBook/MacBook Pro 13 15 17 Early mid Late 2008 2009 2010 2011 2012.etc : Electronics
Amazon.com: DY-tech 2nd Hard Drive HDD SSD Caddy for iMac 20 21.5 27 inch 2009 2010 2011 Early Late : Electronics