As Cookie suggests, there are as many opinions on replacement shocks (and the serviceability of the OEM shock) as there are on tyres, tankbags, huggers and helmets.
It depends on what you want and how much you want to spend.
Start at the cheap end:
Get the original rebuilt (if possible) Ring around via a Google search. Try calling
http://www.mctsuspension.com/about.htm who are very helpful, though they did write a friend's FireBlade off
Find a second hand shock, preferably low mileage, if you can trust the seller's word. You have paid your £12 try the FSW section, perhaps?
Fit a new OEM shock.
Fit a new third party shock. What sort? Anything from the top of the tree, Ohlins, to Wilbers, to Nitron, to whoever...... A search on UKGSer or Google will turn them all up.