New Goals, New Bike?

Let me start with a caveat: I like my bike. It's a good bike and perfect for my biking habits. I ride anywhere from 2-10 miles daily - often pulling a trailer. My Cannondale road hybrid is comfortable and fast. Nate gave me that bike for my birthday nearly five years ago and couldn't have picked out a better fit.

However, as I'm biking more and farther (specifically farther), I'm starting to wonder if a new/used, faster bike would be more suitable to my needs. I'm clueless when it comes to bikes and their strengths/weaknesses. Obviously I know that I don't want a mountain bike, but I don't necessarily need a super fast road bike either.

I can schedule most of my meetings within a five-mile radius of my house. When that works out, I'm lucky. But, there's the matter of one of my long-term clients having an office about seven (hilly) miles away. Within the next few months, I'd like to incorporate a bike ride to our monthly meetings. Additionally, although this is only relevant for the next three weeks, the University of Denver is eight miles away. I would still like to ride to class at least once, but riding to and from a night class in rush hour in the dark doesn't sound appealing. So, I'm a bit stalled until I'm assigned a new class in the fall (hopefully).

That's where you come in: For those of you who ride, what would you recommend for slightly longer commutes? I'm hoping to find something used - either at our neighborhood bike shop or on Craigslist. But recommendations are certainly welcome!