Hiromu Arakawa's Fullmetal Alchemist is a massive influence for me. The way she gives her characters depth and mass is just... wow, she's amazing!
I also love the work of Kiyohiko Azuma on Azumanga Daioh and Yotsubato! His work really influenced how I draw simplified, comedic expressions, and especially how I time my comedy.
Then there's of course Bryan Lee O'Malley, particularly the Scott Pilgrim series, which had a huge influence on both how I draw and panel comedy, but especially how I draw and panel action.
Stuart Immonen is probably my favourite superhero artist. I aspire to his bold, readable figures and clear action. I love his work on stuff like "All New X-Men" and "Nextwave: Agents of Hate".
And finally... Tetstuya Nomura, who, sure I can pretend his character designs on the Final Fantasy series didn't burrow their way into my brain, but it'd be a massive lie because it's really obvious just by looking at how I design and even proportion characters that I'm heavily influenced by him!