Amazon.com currently has deals on two L series lenses for sale.
After instant saving (Add to cart to see lowest price) and mail-in rebates, you can get
EF 17-40mm f/4L USM lens – $639.00 (Compared to regular price at $739.00) – link – Deal Expired
EF 135mm f/2L USM lens – $889.00 (Compared to regular price at $989.00) – link – Deal Expired
This is the lowest price online ever in 4 or 5 years.