I use this one;
http://www.agrisupply.com/m/high-pressure-cast-iron-burner/p/30295/
Nothing fancy, only about 8 bucks, and it has no problem boiling 22 gallons of wort using a 20 psi regulator.
The hop ball outer ring is magnetic and can be held in place with a couple of magnets as shown in the bottom photo. When I used it in yesterdays brew I had the hop ball screen just laying in the bottom, as long as the flow rate wasn't to quick it stayed in place. it wasn't until after the brew...