I went with a Trek XO1. That bike alone is around $1300 from my LBS, but it's an aluminum frame and carbon fork. Quite a comfortable ride.
I also agree with O-Town's comment about the bike alone not being the end of it. I'm commuting in an area (into Hartford, CT) where folks aren't used to seeing cyclocommuters. I need good lights because I'm riding early (typically leave my house ~5:00-5:15AM) and parts of my commute take me through through cornfields where the road has no streetlights. I invested in good, hi-vis clothing and reflective outerwear. Upgraded tires to armadillos, bought a second set of wheels so I can easily put the snow tires on and I'm easily over $2K.