I've had work done at
http://www.difflap.com.au/index.htm on my old CJ8. I was not really happy with the price or quality of work.
On my TJ I get all my diff and gearbox work done at "Diff & Gear Box Industries 2/ 280 Newmarket Rd Wilston QLD 4051 ph: (07) 3356 8397", the guy there is Steve. He likes if you source the parts yourself with jeeps. He is very good on price and does great work. He worked for "difflap" on the southside til they shut down that shop before opening his own shop.
I got my gears off e-bay in the states cause that was the cheapest I could get at the time. Just make sure you get the correct ones for your car.