For your first bike I would definitely stay away from anything over 600cc. 750 tops. Even in the cruiser line. While they may not be the fastest the gobs of torque the larger cruisers have can get you into big trouble really quick. Too often I see new riders go for the big bikes before they have really learned how to ride. It rarely ends well. If you want a naked bike that sits between a sport bike and a cruiser then I would recommend the following:
Suzuki SV650
Yamaha FZ6
Both are well mannered but will giddyup when you want. Insurance is quite reasonable. They can be had second hand for not too bad a price. If these are not the style you are looking for there are others out there in either direction.