[Updated: The price went back up to $595, which is still a solid deal.]
ebay (via AllNewShop) has the Canon EF 24-105mm f/4L IS USM lens for $549 (reg. $999) in limited quantity. Check it out while it lasts here on ebay.
Note: This may be a gray market lens. ebay seller AllNewShop has a positive feedback rating of 99.4% at the time of this post.