OWC SSD Upgrade Kit For 2010 27-inch iMacs, OWC Mercury Electra 250GB 6G SSD, 18" SATA III 6Gbps data cable, SSD Power Cable, Installation tools and iMac screen adhesive tape set :
OWC SSD Upgrade Kits for 27-Inch iMac 2010
OWC Performance Upgrades for iMac 2010
How to Install a 2.5-inch SSD in the SSD Drive Bay of a 27-inch iMac Mid 2010 (Updated) - YouTube
How To Upgrade HDD on Old iMac 27 Inch 2010 Faster SSD Samsung SATA 2.5 - YouTube
OWC DIY Drive Upgrade/Install Kits for Apple iMac Models
How-To: Now's the right time to swap your old iMac's hard drive for a fast new SSD - 9to5Mac