OK, bit of a niche one this but hopefully it will appeal to someone (I know there are a few mountain bikers out there....)
Merlin have some great deals on hayes mountain bike hydraulic brakes. These are likely to be unboxed surplus but they have some excellent deals - I've just order some HFX-9 brakes which are listed at £34.95 each (free delivery). This price is per brake, and the rotors aren't included, and also they don't have IS 160mm mounts at this price.
Best still they have 10% of all orders over £100 (most bike shops are doing this at the moment, chain reaction also are and also have free delivery, wiggle are doing 20%). With 10% of works out under £31.50 per brake, bargain for top quality hydraulics...
NB They also have a decent deal on Shimano XTR dual-control brakes for £135 (£150 - 10%).