IMHO, Chris King is the only headset to put on a tandem... They're not cheap, but they'll outlast your tandem. FSA, Cane Creek, and others also sell cartridge bearing headsets but I prefer to line Chris King's pockets... cool company that has been supporting the tandem community with great headsets and hubs for many years.
Reynolds Ouzo Pro tandem fork? You get the weight savings, some will report that they find it stiffer and/or more comfortable than their cro-mo forks (they are very stiff and the 'feeling' has more to do with the weight reduction than anything magical about carbon), they give an otherwise stock tandem a tricked-out look, and often times allow folks who have a front V-brake and a rear disc to replace the V-brake and Travel Agent adapter with a far superior front caliper brake.