If you are on a close budget a lot of people recommend Shimano. Many people go for the SLX and Deore models as apparently they are just as good as XT. If you shop around you can get a pair with rotors on either side of £100.
If you have a hole burning in your pocket go for Hope. Best brakes in my book, similar power to Shimano but extremely reliable and gorgeous looks and engineering.
Stay away from brands such as Clarks, Avid, Ashima, etc...