There are a lot of different things you can do to strengthen a D30. High strength shafts, ujoints, trussing, etc....The weak point tends to move into the ring gear at that point. A lot of guys will take an High Pinion D30 from an XJ and put it into their TJ's as it will bolt right up using the same knuckles, shafts etc....Plus it gives you a reverse rotation high pinion housing. You could easily run 37's on a setup like that. Another popular swap is a D44 from a Rubicon. Yes it generally does use the same tubes as the 30, but it gives you 30 spline inners and a D44 ring gear.
After that you are talking junk yard or aftermarket for any kind of swap.