If you don't need a new computer now then wait. If I needed a new computer, I would definitely be buying the current iMac or maybe even a previous generation refurbished unit if one with the right configuration was available.
As others have stated waiting for the next big thing (USB 3.0) lost them integrated FireWire.
And while not often Apple has used integrated graphics in the low end iMac. The higher end models have discrete graphics.
And as for Retina, I can see the point in the iOS devices and maybe even some laptops, but you do realize that an iMac screen is already close to "Retina" resolution. Remember for Retina, the pixels per inch is based on the viewing distance to the screen. Move a few inches away from the average viewing distance and voila the iMac is Retina.