Thinksecret has pointed to August seventh as the day that a new revised iMac, as well as a new iPod will be revealed. Newcomer to the Apple rumors gang is 9 to 5 mac, and they describe the new machine on their website:

 What seems to be known about the iMacs is that they will support a brand new metal enclosure which is much more sleek (under 2 inches thick) than the previous revision and lose much of their “chin”. Contrary to popular belief (that the 17 inch version was a goner) they will be available in 17, 20 and 24 inch varieties. The keyboard is also redesigned to be much more mobile and gain additional media controlling functionality (remote control anyone?) - oh and it is RAZOR thin.   

Another website, Appletell.com, says that the announcement will be delayed due to issues with the new keyboard. Whatever the case, it seems like the long awaited iMac revision will be out before September.