The tranny fluid is pretty easy to change. See the Periodic Maintenance PDF in the Powertrain Tech. Ref. thread for a how-to Powertrain Technical Reference Thread
As for fluid recommendations, there is no real answer, every tranny seems to be a little different. For every person that has had good results with Brand X MTF, there is a equal number of people that have had bad results with it.
With that said, I'm currently using Mobil1 75W-90 MTF and it has been OK so far.
GM Synchromesh fluid has gotten some very good reviews, but it is a GL-4 fluid and our trannys spec. GL-5. Nobody is sure of any long term consequences from using a GL-4 fluid.
NEO RHD MTF is what the Subaru USA rally team uses and it has gotten some good reviews.
Motul MTF is what the Subaru WRC team uses. It seems to be a great fluid, but is hard to find in the states.
Amsoil and Redline make a good MTF, but they have both gotten mixed reviews. Some peolpe love them and others hate them.
Your best bet is to start trying different fluids and find out which works best in your tranny for your driving style.
Check this thread for more MTF info Change To Syn Gear Oil Now!