I went to the one in Cleveland last weekend. I've been going to them for the last six years. Like people said, they have pretty much all of the manufacturers there. Sometimes, the manufacturers bring the race bikes. This year, Honda brought Ricky Carmichael's CR250 and a baja bike (I don't follow that type of racing, so I don't know whose bike it was). Suzuki had Brandon Jesseman's bike there as well. Last year, Suzuki brought Matt Mladin's bike, too. If you like street bikes, they also had Ducati, Aprilia, Triumph, Victory, and a few others in addition to the usual Japanese and Harley lineups. The Japanese manufacturers have pretty much a full line of dirt bike models, plus a few quads.
As a manufacturer, KTM was not in Cleveland, but they have been in years past. There was a KTM dealer there, so you could still see and sit on a lot of the current models - 450SX, 250SX, 200SX, 525EXC, etc.
They usually have some sort of show as well. In past years they've had professional trials riders that put on an amazing display. This year, they had an act where they have two or three riders in a steel ball circling around, and a kid who does a backflip on a minibike ramp to ramp. It was interesting in a carnival sort of way.
Some accessory dealers, but mostly geared towards street bikes. At least in Cleveland, they sell beer, too.
I think its a great time.