How big of a motorcycle should I get?

I am a big guy, 6 feet 4 inches tall and weight 300lbs. I haven't rode a motorcycle in 17 years but do to the gas prices, I want to get back into riding for daily commuting to work. I plan on buying an older, less expensive bike. However, I don't want to look like a gorilla on a tricycle either. I don't really care about style or engine size. My main concern is to not get a bike so big I cannot control it. Alot of people say beginners should stay away from liter bikes, but the 600's look and feel to small to me. The sales guys at the shops just try to upsale as big of bike as you can afford, but offer no information on what exactly would be best to learn on. 17 years is a long time to be off a motorcycle. I was alot younger and reckless when I was younger. I have a family to take care of and really don't need to get killed because the guy at the Harley shop thought I needed a 1800 cc bike because I am a big guy. Any opinions or thoughts?