Turbotune for X-Trail or other common rail diesels:

[Piglumps]

http://www.energy-tuning.com/turbotune-for-cars-4x4s/

This unit increases power and torque with 9 different settings in the firmware, simply plugs into the common rail connector.. I got 25% better fuel consumption towing a 1400kg caravan, plus it was smoother, quieter and went like a ferret up a drainpipe with a firework in it's botty! Looking for £90 inc postage. Can be reconfigured by sending it back to the makers who put a new lead on it and reinstall the maps for the new car for £29.99 ..

[Gassoon]

I really fancied one of these for the old Citroen common-rail, heard great things - but never got around to it...

[Piglumps]

Apparently you can send it back to the maker and they will reconfigure it for a different engine...

[Gassoon]

Too late for me though, sold it last year...