Zen
here are some options - both with standard springs etc - just make sure you set the pre-load correctly - shims for the rocker arms are 20 quid a set.
Viper hurricane is outstanding in the mid-range but only available as a long-nose for dizy engines - fantastic value at only £160 quid
If you have a GEMS or Bosch engine with auto box engine then the Kent H180 is pretty fantastic - massive wallop off-idle - good mid-range - is also available as long-nose - cost is about £230 from Turners.
Having had such positive experiences with both of these I haven't gone elsewhere although I hear good things about the piper torque max also.
Have used 4 hurricanes and 4 H180's on various engines this year.