Dingham Autocouplers
The Dingham Autocoupler is probably the least obtrusive commercially available automatic coupler for model railway vehicles in 7mm scale (O gauge) and 4mm scale (00, EM and P4/S4). It also has the advantage of a delayed uncoupling action without the need to move the shunting loco back and forth to operate the delay mechanism.
http://www.dingham.co.uk/index.html
Fine Trains On30
FineTrains (O, On30, On3, On2) fully built original design craftsman models.
http://www.finetrains.com/
C&L Finescale
&mm & 4mm Model Railway Track Components
http://www.finescale.org.uk/