A good beginners bike is one that is lightweight, easy to manuver, and has manageable power. It is generally a used bike that has plenty of life left in it. I am sold on the older 400/450 standards from the early to mid 80s for just this very purpose. The bikes weigh a couple of hundred pounds, sure styling wise they leave a lot to be desired, but they are cheap-around $1000 all day long in good running shape. They were sold by the kazillions and there are still millions of em around on the roads.
The 400/450cc size is a great engine, not too powerful, but can do anything that the newer bigger bikes can do, just not as comfortably, because of the generally cramped riding position-easily remedied with the addition of some highway pegs. They will run virtually forever with routine maintenance and are very easy to maintain. The biggest thing is to remember to lube the chain every 500 miles.
All the japanese manufactors made them-Honda, Kawasaki, Suzuki and Yamaha, with the majority of them being either Honda CM400/450 and the Yamaha XS 400/450. The Kawasaki EN450LTD is a 454 cc inbetween styled bike, that helped bridge the gap between the classic style and todays cruiser style. It has belt drive which does not require any maintenance except periodic adjustment to the belt. The engine was later bored out and became the En500 Vulcan which is still available and with a few mods, became the EX500Ninja engine.
