Canon has announced a price cut on many of their "L" series lenses (and a few others). Price drops range from $1000 for the high end long telephoto lenses to a more modest $50 on some of the less expensive lenses. Astute readers will note that this price drop coincides with the end of the recent "instant rebate" program. The new lower prices are typically around those previously seen with the rebates (maybe a few dollars more), but these price drops are permanent - or at least until there's another price rise!
Given the new lower prices I would not expect to see a rebate offered on any of these lenses anytime soon. There are however a lot more lenses whose prices haven't dropped and so might more reasonably be expected to be offered with a rebate at some point.
Since Canon are fairly strictly enforcing their MAP (minimum advertised price) policy, you probably won't see any addition "street" discount on Canon lenses. You may see some "packages" though that include something like a free filter. Check around. Adorama have a number of such deals For example They offer a Canon EF 50mm f/1.2L USM Ultra-Fast Standard AutoFocus Lens Kit, USA with 72mm Digital Essentials Filter Kit, Lens Cap Leash, Professional Lens Cleaning Kit for the same price as the lens alone. Adorama also offer a 2% store credit on future purchases on most Canon lenses, so that's $20 on a $1000 lens, $200 on a $10,000 lens.
The best deal might be the EF 24-70mm f/4L IS USM with a price drop of $500 (33%)from $1499 to just $999. On top of that there's an additional $250 mail in rebate if you buy the lens along with an EOS 6D, 7D, 70D or 60D.