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At the moment I carry my gear in an old and rather battered-looking ordinary backpack, everything wrapped in its own padding/bag to stop it rattling around, filters in he side pockets, etc.

Summer's a'here in Europe, and I'm looking for a decent dedicated backpack to carry the camera body with medium zoom fitted, a wide angle lens, telephoto, flash, small portable storage unit and various other bits and bobs (spare battery, cards, filters, etc.)

I don't need space to carry a laptop as I don't have one.

However, I do want a bit of extra space for carrying a rain jacket, water bottle, etc, as I walk in the mountains a lot. Facilities for carrying a lightweight tripod would also be useful, but not essential.

Can anyone recommend a make/model? Please note, I live in Europe (Switzerland) so US-specific models will probably be out of reach for me.

I have been using lowepro computrekkerAW and been happy with it.
to my experience it offers plenty of room for variety of equipment while with it's solid design it offers good  good protection to your gear. as far as I know it is already durable to rain but if it is heavy rain you can also use the all weather cover (sort of a rain coat I'd say:) )
it also comes with a compartment for a laptop which you can use to store some other stuff if you don't need it ,I almost never carry my laptop but since it is a long lasting bag you never know may be you might need it in the future..
http://products.lowepro.com/product/CompuTrekker-AW,1924,16.htm

Im using the same backpack , and its great , but sometimes if find it a bit too big for my needs on the field , especially on long walks , climbing etc  , cause Im not using all the space it provides , I mostly carry 3 lenses and one body.   I will buy something smaller in the future but I will never get rid of this model , cause its great for long trips , and I have to say its the most comfortable back pack I ever tried.   

Lowepro slingshot might also be good for you. Switching lenses and getting the camera from backpack is very easy. Here's a video about it:

<a href="http://www.youtube.com/watch?v=h4mmqSU_Mxw" target="_blank" class="aeva_link bbc_link new_win">http://www.youtube.com/watch?v=h4mmqSU_Mxw</a>