the newer jeep cherokees have D44 front an rear but it cost $$$ to get some or you can do what HMFI said about getting them at mopar but thats also big $$$. izuzu 4x4s have d44 rears but they are smaller width then yj. i took a D44 out of wagoneer and converted it to coils from leafs and put an 8.8 in the rear and it seems to be working out good.
or you can pm kinslayer on here cause hes rocking D44 front an rear in his cherokee
for similar size (width) axles the grand wagoneers from the 80's are a good swap. not all wagoneers had a d44 rear (amc 20 is very common) and some also have the same kind of vacum actuated 4x4 engagement on the front axle like the YJ's have. I would to avoid the vacum style front axles
Asking that question means that you are planning on doing some serious work to your Jeep.
Asking that question also means that you haven't done enough research... search, search, and search some more. You'll get better answers from pages like www.jedi.com and the various 4x4 sites with articles and writeups than you will from asking vague questions on a forum...