This one is obviously still very much in rumor territory, but a couple of separate reports have cropped up today that suggest Apple could be set to debut some updated iMacs as soon as next week. That includes a report from 9 to 5 Mac that iMac orders are being delayed until May 2nd, despite the fact that they're still listed as shipping within 24 hours on Apple's website, and a separate confirmation from a trusted source of the site, who says that Apple will stop shipping iMacs to retailers this week in advance of next week's supposed release. That's further backed up by a report from Mac Rumors, which cites another source who says that Apple will be changing the promotional materials in its retail stores for a launch on Tuesday, May 3rd. Details are comparatively light on the rumored new iMacs themselves, but the safe money seems to be on Sandy Bridge processors and Thunderbolt ports.
AppleiMac 27-inch with Retina 5K display (late 2014)