Cdale RT2 is a $3,549 6061 aluminum-framed tandem that comes in a single color (white) and four sizes with Ultegra components, a good conventional wheelset, FSA Gossamer cranks, Avid dual discs, etc. and is now made in Asia.
Pros, C'dale has traditionally delivered a lot of value for the money and the quality/performance of the US-made, batch-built tandems has always been excellent. Customer support has also been good.
Cons, C'dale shut down their US manufacturing factory last year and moved 2011 model-year production off-shore without moving the price-point of their now lone tandem model. C'dale dealers aren't typically knowledgeable about tandems unless you happen to buy the bike through a tandem speciality dealer who offers C'dale tandems as part of their line. Not sure if the new owners of C'dale have mucked around with the tech support centers or not, noting the tandem expertise in the tech center has diminished a bit over the years.
Co-Motion Torpedo is a $4,300 Reynolds 853 steel-framed tandem that is available in 30 different color and two sizes where both the pilot and stoker riding positions are height adjustable for a very wide range of different cyclists also with Ultegra components, a very good conventional wheelset, FSA Gossamer cranks, Avid dual discs, etc. and is hand-made to order in Eugene, Oregon.
Pros, The Periscope frames are size adjustable, which means it's a tandem that grows with families or allows a wide variety of different folks to ride the same bike without compromising on a good fit. It's available as either a 26" or 700c wheeled model, you get to pick your color, they're only sold through dealers who know a thing or two about tandems and/or supported by easily reached folks like the owners of the company who are involved in the day-to-day operation and building of the products. They're made in the US by a small number of craftsmen in Eugene, Oregon and the quality and performance is about as good as it gets. These are hand-made, not mass-produced.
Cons, it costs a few more bucks.
This is just a snap-shot of off-the-cuff stuff that comes to mind. Each of these tandems are very different in terms of what they are designed to do and will even handle a bit differently, where the true pros and cons or goodness and badness of the differences is subject to individual tastes and needs.