When I bought my 40D, I also bought a screen protector, the size is bigger than the rear screen so what's leftover, the salesperson custom cut and apply on the top screen for me.
think there is no custom size for 40D, so it u want to save a bit, go to Daiso and buy a few piece of the bigger size ones and cut to fit yourself. The quality of the protector is quite good.
there are many screen protector that offer exact fit for 40D's 2 LCDs. one of them is ZAGG, US$15 include free shipping from US. another is Martin Fields, SG$24.95 + SG$2.95. if you don't mind the quality, ebay have a lot.
personally, I will go for invisibleSHIELD. cheaper, durable and proven to last. I have quite a few of these shield on my camera and mobilephone, none of them have any damage so far. the delivery might take 2~3 weeks though and applying need patience...