Jon Hall [flickr] -Jon creates amazing aircraft. His highly detailed and imaginative MOCs are well worth the study.
Dag [flickr][blog][brick owl] – Dag is a member of my local LUG. He has a lot of microscale MOCs and blogs about building techniques.
Waka [flickr][blog][youtube] – Another fabulous builder in Japan. He blogs about his creations, sometimes showing the details of their construction. Most of his MOCs are mecha or sci-fi, but he has some cool characters as well.
Zi Zy [flickr][blog] – One of my favorite mecha builders. His creations are intricate and steeped in anime sensibility. His blog is in Japanese. He has published a number of books on building, but they are difficult to get outside of Japan.