This is probably the simplest design that I've come across. http://www.backyardmetalcasting.com/oliverburner1.html
And, being a simpleton, I built one in less than an hour. It's the only burner I've ever built, it's the first burner I've ever built, and it's probably going to be the last burner I'll ever need. After a little tweaking my forge was reaching 2000 degrees without so much as a hiccup. Good luck with whichever design you go with.