Sean Connery - Goldfinger
Sean Connery's best performance as Bond, as well as a great villain and great locations. A lot of fun to watch.
George Lazenby - On Her Majesty's Secret Service
This was a tough choice.

Seriously though, this is a great Bond film. My second favorite overall next to Casino Royale.
Roger Moore - The Spy Who Loved Me
Just awesome. Great action and stunts all the way through. It also has, in my opinion, the best Bond girl.
Timothy Dalton - The Living Daylights
Before I probably would have said Licence to Kill, but after watching this recently I realized how much I really enjoy it. The pre-credits sequence and John Barry's score alone make this a great film.
Pierce Brosnan - The World is Not Enough
Despite it's flaws, I love this film. I think performance wise, third time was a charm for each actor (with the obvious exceptions of Lazenby and Dalton, and Craig for now). Brosnan looked like he was really enjoying playing Bond in this one and gave a great performance.
Daniel Craig - Casino Royale
My new favorite Bond film overall, at least until Bond 22 comes along. Daniel Craig's performance was flawless. I can't wait to see where he goes from here.