Time for the third round of Castle Masters (TM). Photo above is WIP photo of DarkWater Keep.
Dan G at MOCpages Link Build called "Little Keep" but not so little.
Nathan (Norro) Todd hangs out at classic-castle forums. First inspiration for me to build a waterfall scene. Brickshelf Link Theres also a little known waterfall scene called Apocalypsis. My WIP definitely isn't influenced by that at all though.
Patrick Bosman at Brickshelf Link This one is called the necromangers tower I believe.
Adrian Florea, at Flickr Link This one is called Nedleh point
Hippotam (Marcin I think) only has a couple castle builds but operation lethal duck is a must see: Brickshelf Link
Wilson Raska - Valkayria: A very impressive rock called Asguard. Some other impressive builds can be found on his brickshelf Link
On of my personal favorites isn't a castle at all, but one of these Schlimps Elephant Link
I just found this one today browsing though the Brothers-Brick archives: Chris Edwards Island 3. Wish I saw this earlier becuase I'm great at stealing ideas and using them as my own. Flickr or BrickShelf. Note there are different builds in the different links.
torgugick built the Taj Mahal etc that everyone knows. Also has some good castle stuff. Link
As you already know, I love the mumak. My fav is the tower. It somehow reminds me of Rivendel, for some reason. Also, the HUGE one on top of that is also very well done. If only we all had that many pieces, this would be a much different website... Many better MOCs.