I also like Ski Doo. We have 2 adult size sleds. I did have a optional seat for one, that would allow 2 people to ride comfortably, but there are only hand holds on the rear sides of the seat. They have a model that can come with 2 seat with a back and handles on it. (GSX I think). A 600cc engine sled would be plenty.. They also make a 500 air cooled , but the 600 E Tec is very user friendly. Tried to link their web site but the server was too busy in the US.
www.skidoo.com..
We also have 2 smaller sleds for the kids. Made by Yamaha, there 1991 models. There where 2 sizes produced, a Sno Scoot (80cc engine) and Sno Sport(125cc engine)..
The Scoots can be found on craigslist and ebay...Great for the kids riding around the house.
http://www.yamaha-motor.com/sport/epic_snow/1988_snoscoot_small.aspx
It's a great sport, but very weather dependent, both good and bad.