If you could answer these questions, I think it would help people start to suggest some bikes.
1. How far is your commute?
2. How hilly is the ride, and what's the terrain like?
3. What's the range of weather you see yourself riding in?
4. Would you enjoy working on the bike yourself, or would you just bring it in for occasional tune-ups?
5. How much of a priority is speed?
6. Do you ever have back or neck pain/stiffness?
7. Could you park the bike inside, or would you lock it outside?
8. What's your budget?