According to some analysis over at Three Guys and a Podcast, Apple typically pushes out a refreshed iMac every 8 months and a major update every 27 months. The last major update was in October 2009 and the last refresh was in July 2010. The report notes March as the likely month for a minor refresh to the iMac line. We’ll probably be seeing some new MacBook Air-like SSD drives, new storage options, and of course new processors. Cheaper iMacs with a new screen size too, if we’re lucky.
Blu-Ray and touchscreen? Unlikely.