Ummm, how has noone mentioned the true pixel master and pixel theorist, HELM!
I personally love reading every line he writes. It seems like he puts so much thought behind everything he writes and does. His writings on pixelling are really what got and keep me interested in pixel art and to me show that debate like that is the future of pixel art. His pixel art is at the same level of quality. Every new piece impresses me more than the last with its interesting technique and beauty. He is masterful with restrictions and most facets of pixel art. I still use his 4 colour spartan piece to introduce people to the magic of pixel art. He is a true inspiration.
Another artist that needs some love is Adarias/ndchristie (I believe he goes by on this forum). He is similar to Helm in that he experiments with different styles. His use of colour in a piece is really masterful.
Facet! One of my true favorite pixel artists, that I dont believe I have ever even seen a completed picture from. He is the edit master. Him and pistachio's edit of delicious' werewolf way back are what cemented in my mind that I love a sketchy style. The look facet achieves with a few calculated strokes exceeds most pictures I see in a day. There were so many beautiful edits of his I was hard pressed to choose one to put here. I have a link of all his edits in a gallery he gave me if anyone would like it.
Ryumaru, the resident anatomy master
If I could find a small picture of his anatomy practices it would be here. Check them out though, they are great.
AlexHansonWhite, another inspirational artist that develops theories as well. I love his work.
PPD, must've sold his soul to the devil for those animation skills.
Come on, we've all seen ppd's animations we know how great they are.
(I didnt mean for this to turn into a list
)