After spending 2 hours just pressurewashing treesap and muck off my car, I decided I needed to get a decent cover.
I've used care4car before to buy Rain-X (which I'm still not 100% sure about), and a cargonet to keep loose items secure in the boot.
http://www.care4car.com/productdisplay/productid/198/Waterproof_and_Lined_Full_Car_Cover.html
At £48 it's a bit steep, but it's supposed to be waterproof and has a soft lining to protect the car.
It's also got a nifty carry-case and also turns out to have a slip case you can put it in too.
The outer material feels quite tough, and the inside is a weird soft material that looks like a thin layer of felt.
There's elastic at the front and back to help it cling under your bumpers.
Sadly due to having a lower front and rear bumper it doesn't quite hang down perfectly, but it's still very good for the length. I've got the Large one, any bigger would be too big I think... but then you might need the extra length if you've got a big spoiler...
There's mirror pockets and also a nifty zip opening so that you can still get to the driver's door.
1 reinforced eye on each side (at ground level underneath the rear quarter windows) can be used to tie the cover to a wheel to stop it blowing off... or i guess you could thread some string under the car... but that might be a bit too much hassle.
I can't comment on it's ability to fend off the weather as it's currently dry and sunny, but it looks good so far.