ebay seller deals-all-year has a 99.8% positive feedback rating on ebay. The listing notes that you can register this lens for a 1-year Canon USA warranty.
ebay (via 6ave) has the Canon EF 24-105mm f/4L IS USM lens for $639.99 (reg. $1149). Check it out here on ebay.
Note, this is likely a grey market item with an in-house warranty from 6ave, which has a positive feedback rating of 99.3%.
[UPDATE: These are all gone now at the deal price now. It's back to $1149.]