The shop that never has a sale!!
And don't buy any of that flight planning cr*p such as 'circuit planners' and all that nonsense. If you can obviously buy it somewhere else then do so (watches, timers, 'comedy items', etc).
Kneeboards spring to mind as another great rip-off. Take a piece of board, and a paper grip, cover with aviation related information such as morse code, and hey presto! up to 30 quid!
How about torches for up to 35 pounds. I got one for 3 pounds from my local petrol station, including batteries. Although it was !!!!! mind you and did not last long.
My favourite though has always been the partial panel stickies. These are basically round post it notes, and cost 5 quid for 100.
Most reference materials required for flying can be found for free on the web.