Earlier this week, Apple announced that the iMacs it announced alongside the iPhone 5, iPad Mini, and iPad 4 would go on sale on November 30. Just in case you haven't looked at the calendar in a while, tomorrow is December 1, which makes today Friday, November 30. If you're holding out for the 27-inch model, you'll be waiting into December, as Apple still hasn't announced a formal ship date for that version. You can order one today, anyway, it just won't ship in the next few days.
The 21.5-inch iMac is available with a 2.7 GHz quad-core Intel Core i5 with Turbo Boost speeds up to 3.2 GHz, Nvidia GeForce GT 640M and 8GB of 1600 MHz RAM. Alternatively, you can upgrade to a 2.9 GHz quad-core Intel Core i5 with Turbo Boost speeds up to 3.6 GHz and NVIDIA GeForce GT 650M. Pricing for the 21.5-inch iMac starts at $1,299. Bumping the processor and graphics card will put the price up to $1,499. Apple says shipments for the 21.5-inch will go out in 1-3 days.
As mentioned previously, Apple still hasn't offered a solid release date for the 27-inch model. At least, they've offered nothing more specific than 'December.' However, the website now says orders for the 27-inch model will ship in 3-4 weeks, so you should get your computer by New Years if you're ordering today.
Just to refresh your memory, the 27-inch comes with a 2.9 GHz quad-core Intel Core i5 with Turbo Boost speeds up to 3.6 GHz and NVIDIA GeForce GTX 660M for a suggested retail price of $1,799. You can also bump the specs in this one, pushing it to a 3.2 GHz quad-core Intel Core i5 with Turbo Boost speeds up to 3.6 GHz and NVIDIA GeForce GTX 675MX. This will push the price to just a hair shy of $2000.