I really liked the 2005 Jefferson Nickel with the Buffalo reverse, that was my favorite 21st century circulation release.
Actually, now that I think about it. My #1 favorite 21st century design is the First Lady "Jefferson's Liberty." Does that count? That coin is just gorgeous.
Burnished dye There's a beauty to the Silver Eagle burnished dye that isn't duplicated anywhere. I mean the coin itself is a winner, but with the muted glow to this burnished dye finish, you just can't beat the joy of looking at it. I didn't think the mint could create anything to rival the proof Silver Eagle, but this one stands right beside it.
As far as commemoratives: I liked the 2006 Benjamin Franklin dollar. Not the scientist one but the other. The 2001 Buffalo was good and I also like the 2008 bald eagle half. For circulation: The 2005 buffalo and the westward journey series in general was really good also.
I have always been partial to the Leif Ericson commemorative Dollar. I love the font of the lettering, the portrait is awesome, and anytime they put a ship on the reverse of a coin it is successful. Speaking of ships, The 100 year anniversary of the sinking of the Titanic is coming up in 2012. I think that would be an excellent idea for a commemorative coin.
I also like the 2005 Jefferson nickel with the buffalo reverse. However, I am ready for the old portrait of Jefferson to be used again.