GreatLakesOffroad is the beefiest one I've ever seen. My brothers D60 one made by them is 1/2" thick, with a 1/2" thick strap going down the center of the cover, (running the length of the ring gear) for a total of 1" thick right there.. He did have to do some grinding because he had tie-rod clearance issues because he isnt running high-steer.. The only downfall I would say with it, is he had an 8 week waiting period to get his. You may or may not.. But as far as I know, he build them when he gets an order..
You can see his in the attachments... Other than that I would reccomend BallisticFab, BlueTorchFab, or RuffStuffSpecialties.