Heavy Duty Tires

There is plenty of stuff on here about heavy duty rims, but what worries me about my wheels is the tires. I know the higher the PSI the tire the better it is, but does any one have recommendations for a decent heavy duty tire? I run 20 inch wheels so I know there should be plenty of options, just wanted to know if anyone has experiance with one tire or another. Ideally I would love to use a moped rear wheel, but as the budget doesn't allow it I'd be happy with tires that I feel comfortable butting 300+ pounds on and cruising around at 15 -20miles an hour.