If you want something really loud and showy, go with a motenergy/etek type motor driven to the rear wheel.
Those are designed to be ran on sine wave controllers, but when run on square wave controllers, they've got a nasty audible bite.
Every etek/motenergy motorcycle video i've seen on youtube has sounded freaking mean.
For a hub, the cromotor does come in motorcycle form, 180-200mm axle and motorcycle brake and all. You can find that motor from greentime. It's rated for about 4.5kw continuous, so on a motorcycle, your reasonable top speed would be 50mph continuous, with a decent amount of thermal headroom to do probably 60mph tops for a few miles.
John in CR's scooter motors are pretty cool, but the optional rims are quite small, designed more for a scooter than a motorcycle.
How much power are you looking at running? You may want to look at getting a better frame as the cost of the electronics to run the bike properly would be ~$2-4k depending on range. Building the bike on a junker really hurts as i have come to realize with my motorbike build.
