I won't recommend any cases. Except the occasional blizzards I guess.
In cold temperatures, the batteries will not function well. But a run of the mill case will not solve this problem either.
In extreme cold (arctic/antarctic), specially made electrically heated jackets can be bought, but at that level I would venture to guess one wouldn't be bringing a 450D, but a Mark II or Mark III, which are much tougher and can withstand a lot more "naked", not to mention have a lot more professional protection gear (at a horrible premium prices).
I would venture to guess that "weather proofing" your camera against rain or sandstorms is your primary concern. My opinion is that situations where I felt uncomfortable with my old "walking around" FILM Canon EOS4 in the "nude" is rare, and in those cases I simply used 2 heavy duty "CLEAR" garbage bags with a hole for the lens where I've secured using the lens hood's threads. The eyepiece is also another hole with the rubber piece holding the edges. I have also in 1 occasion wrapped the whole camera with the material but also allow changes of film by masterfully applying silver duct tape (thank you Red Green Show).
Rest of the time I trust Canon construction. Obviously the 450D is quite a bit more frail than the EOS4, but I believe it will hold up in moderate weather.
The case you've shown above will definitely not guard your camera against heavy rain or sand. Remember that you still have to "decase" the camera to use it. There are professional grade weather seals kits for SLR and DSLR cameras, but those are custom orders (and cost more than I think is worth it for the few times I thought I needed it, see above "solution"), and I simply never bothered with them.
The only thing that the case you've shown will benefit you would be to make you look "professional" to the amateur or semi-pro, and amateurish to the real professionals.
MEANWHILE, congratulations on your purchase of an EOS 450D. I have just bought one for my digital walking around needs. It is also my 1st purchase of a DSLR (in my line of work, I hire photographers with REAL digital gear to do my "bidding", and have just recently abandoned film photography as my main hobby due to cost of processing and neg-scanning). It is by far the best semi-pro camera in the price range. The pixel count is astonishing at this level, and the new large LCD is quite a beauty to look at. A gem if you coupled that with its low power consumption (unless you shoot with the LCD as the viewfinder or "LiveView" I think it's called, which I think is unnecessary other than to make guys moving up from Point and Shoot digital cameras a bit more comfortable with DSLRs).
I've also bought a cheap 75mm-300mm 4-5.6 EF III USM lens, even knowing the lens' flaws (I actually like the lens, not just for the price, but it does have a few "quirks" that needs to be kept in mind if you want to take usable pictures with it). I am just using it to bridge the gap before my compact film gears arrives from Shanghai with my other EF USM lenses.
On the bag front, I bought it in China and there seems to be a promotion here where Canon gave out a large bag with each purchase of the 450D before July 27th (see attached picture) or bag and monopod for the higher series.
I've just picked up the bag from Canon today after waiting for a week for it.
The bag is nice and can hold quite a lot, including my 15inch Macbook Pro, and comes with a mesh bag for the wires. After my 4 other EF lenses arrives, I suspect I should be able to fit them all comfortably in this bag once I have the time to actually set the flaps in their correct positions.
I walked around all day with this bag (in moist South China heat). And it feels very comfortable despite its size.
I have used the Toploader for a few years, and I do like it a lot also, but since I don't need to look stylish, or do a lot of hiking, I find this new bag better suited for my purposes, which is to keep the maximum amount of my gear in one package for easy access, rather than a lot of everyday/outdoors/rough usage.
I would try to inquire if Canon sells this bag to consumers.
Time to put the Pelican Hard Travel Cases I had before in the closet for when I need to fly again with my gear.
Just my 2 cents.
One can keep a camera for days out there as long as the batteries and the camera are allowed to warm-up a little. I know of some photographers from the local university who have taken their Canon cameras on expeditions on Mount McKinley. They keep their cameras in packs like I mentioned, and place a couple of extra batteries in a small case next to their bodies. They circulate batteries from the camera to the pocket, and back. What happens to the battery when it get cold is that its capacity is reduced (not discharged).
