check out the xtracycle
xtracycle.com
it's adaptable to any bike and allows a huge load. Weighs under 10 pounds and rides just like a regular bike.
I'm putting a freerider on my Novarra Buzz (26" slicks) with a added 50 for cruising and a clipon aerobar for cutting into the wind.
It's a heavier bike, but good for dirt road touring and i can throw a full size backpack on one side and bike touring stuff in the other and ride to hiking spots, overnight camp somewhere up a mountain and ride home the next day.
I can also pick up cute hitchhikers too, (dreaming)