Take a look at the tandems built buy Burely, Trek, cannondale and KHS all good bikes that will give you years of service. These bikes are in the $1500 to $2500 price range, if you want to spend less try looking into a used tandem.
Most of the recumbent tandems start around $3500 to $4000 and go up from there. Sun offeres the EZ tandem for around $1800.
How you plan on using the bike should point you to the bike that will serve you best.
You can find lots of infomation on the web, a good place to start is http://home.att.net/~thetandemlink/
"When the spirits are low, when the day appears dark, when work becomes monotonous, when hope hardly seems worth having, just mount a bicycle and go out for a spin down the road, without thought on anything but the ride you are taking." - Arthur Conan Doyle