If you are talking about add-on eletrical heaters, I've heard good things about one of the ones sold by 4 Wheel Drive Hardware, but their website seems to be down right now.
But the other big vedors, such as Quadratec, Leon Rosser Jeep, and Wilson's 4x4 all sell heaters.
'82 Scrambler - NV4500/4.5" lift/33" Toyo MTs/4.0/twin stick, and my windshield washers work! Full 1/2 cab Cage
2004 Grand Limited 4.7 HO - OH Boy!
2010 Grand Laredo 5.7 Hemi - SICK - work vehicle -gone - replaced by an 08 Tahoe - nice ride.
"Both my Doberman and my Jeep can accurately be described as 'black and rust.'"
"I got a fever . . . and the only prescription is more cowbell"