What is the best design for dual extrusion on reprap prusa mendel ?

What is the best design for dual extrusion on reprap prusa mendel ? I just bought a second J-Head and I’m about to buy another Nema 17 motor. Right now I’m happy with my Wades-reloaded extruder, but I did not find a dual version of it on thingiverse.
Anyone who can recommend a good dual extruder design ?

Is this an actual J-head or one of those cheap knockoffs? That one looks like an MK-IV-B.

yes, its a MK-IV-B. Bought it here: http://www.2printbeta.de/product_info.php?products_id=119

An interesting project at http://reprap.org/wiki/RUG/Pennsylvania/State_College/Software/Parts/Dual_Extruder is looking at mounting two extruders on a single carriage. It has STL you could print now. I can’t quite see how the holes line up with the extruders.