The Canon 24-105 f4L IS USM lens is bundled with some of the more advanced Canon DSLR kits. Some enterprising retailers are taking advantage of the kit bundle discounts and they sell the camera and the lens separately, partially passing some of the savings to the lens buyers. Once such case is found in the eBay Deals where eBay seller “Get It Digital” (99.5%) is offering the white-box (does not come in outer retail packaging) Canon 24-105 f4L IS USM lens for $606 with free shipping, with a limit of 3 per customer. Over 1400 lenses got sold so far from this listing per the eBay statistics over there.
NOTE: the eBay listing has no mention of a warranty. It does not state whether the lens was split from a USA warranty kit, or if it was split from an Imported kit. To be on the safe side, assume this is an imported grey-market item. They would have probably charged more if it was a USA warranty lens.
The lens on its own in retail packaging with Canon USA warranty goes for $1000 at authorized Canon dealers (eg Adorama with boatload of free accessories). A white box option (again with no specifics on warranty) goes for $610 by AudioDealz fulfilled by Amazon (with six free lens-related accessories).