Just finished the O'Brian series myownself a few days ago. Also for the umpteenth time. I love the way he writes. There are a couple of other books he wrote prior to the Aubrey/Maturin series that are interesting, Not prequels but an idea where the A/M series came from - "The Unknown Shore" and "The Golden Ocean". Good stuff.

Starting (again for the umpteenth time) the Lucas Davenport 'Prey' series by John Sandford. On book 2 right now. Also good stuff.