I've got a nearly new Lowepro Slingshot 100AW bag for sale; great camera bag that can be worn as a rucksack but easily slung around for acces to the camera.
I now have too much in the way of
crap lenses so I've gone for the bigger model. It will take a DSLR and mid range zoom plus a couple of extra small lenses plus pockets for flash, memory cards, cables, condoms, whatever else you need to carry
http://www.jessops.com/online.store/categories/Accessories/Bags%20and%20Cases/Backpacks/products/Lowepro/Slingshot%20100AW-34700/Show.html£69.99 from Jessops, its almost new - only been used half a dozen times - perfect working order. Really comfortable to wear and easy to use.
£25