Ive seen many many topics covered about this so im pulling all the information covered in the topics into one:
Sony:
Autoleads: http://www.autoleads.co.ukwww.autoleads.co.uk do adapters for the stalk but none for the display, currenty trying to get one for stalk and display that works, rip speed do them for £30 but you have to remove your dash to fit it.
Connects2: http://www.connects2.co.ukwww.connects2.co.uk do adapters for the stalk and display, the only lead that works with the display, ripspeed sell them for £60. Normaly have to be ordered in i was told, also the easiest to fit. No removing dash, it simply uses the Remote Port, Power & CD Changer Controls.
Audiolinx: http://www.audiolinx.co.ukwww.audiolinx.co.uk do adapters for the stalk and display, ive never heard anything about them but http://www.incardiscount.co.ukhttp://www.incardiscount.co.uk stock them for £60.
Kenwood:
Justkenwood: http://www.justkenwood.co.ukwww.justkenwood.co.uk stock the adapter for the stalk control only, very much alike the autoleads one for fitment and controls.
Alpine:
MCS Direct: http://www.mcs-direct.co.ukwww.mcs-direct.co.uk stock the adapter for the stalk control only, Its under Alpine|Accessors, in 2 parts. You need the control unit and a interface, cheaper then ordering it from Halfords. Again fitment is like the Kenwood and Autoleads Sony adapters. Shame alpine only offer stalk control only.
Blaupunkt:
Blue Spot: http://www.bluespot.co.ukwww.bluespot.co.uk stock the adapter for the stalk control only, no display. £44 and fits like the Alpine, Kenwood & Sony Autoleads ones.
If anyone one has anything to add or if ive missed anything please add to it.