In reply to The Lemming:
If it is just shopping and around town stuff you want to do, how about this rear side wire basket from Basil, for 15 pounds or so, instead of a pannier.
http://www.amazon.co.uk/Basil-Rear-wheel-basket-Cardiff/dp/B005CGLFOM/ref=s...
We have ortlieb, Altura, and a fancy Dutch make of panniers for touring, of which the ortliebs are the best; but for just shopping; the basket is way cheaper and a lot handier.I use it all the time. I just hook it onto my rack, then unhook it at the shop and use it as my shopping basket. it is easier to carry around than many panniers and the lack of a lid means it is also easier to chuck stuff into it then get it again once you are home.
I also use it for going to my allotment on my bike, or to the pool. Wet and mud don`t collect at the bottom of it but just fall out. At first, I used to attach it securely to the bike with a bungee, but haven`t bothered once I realiised that this is unnecessary and that it would be a lot handier without.
They make smaller front baskets too, and I want one.