A stainless steel patio heater:
I noticed a heater like this on a neighbor's roof deck and I thought it was a brilliant device. The heater provides a circle of heat about 20 feet in diameter, which is large enough to heat our patio.
Smith & Hawken has a gorgeous industrial-use one but it's $500. The one pictured is from Home Depot (the new one on W. 23rd St. is actually sort of nice and doesn't smell like sawdust) and is $200 less.