As far as Disney Club discounts go, my understanding from previous posts and from DU is that room only discounts are only available by calling them directly, not through DU. DU does offer DC discounts on packages though, which is what I did last October (saved about $100!).
Though I'm not a fan of WDW packages, I really like the DL ones. I've used them several times, some at Good Neighbor Hotels, and most recently, at GC, and I've always come out ahead as opposed to piecing together everything myself. And the things in the packages are practical things that we made use of.
I think discounts at GC are hard to come by in general, because it's so new, and it seems to be very popular right now. I've seen a few on some of the sites Teri mentioned, but I think you have to be flexible with your dates to use them.