Hi guys, I'm back, and I'm looking for some more advice... =)

I borrowed a cheap mountain bike to commute ~10 blocks around the West Philadelphia area, between 30th and 40th streets. Now, I have seen the light! Walking definitely sucks...

I'm looking to invest a bit more in a road bike or a hybrid (less chance of getting flats?) ~$500, but this limit is semi-flexible depending on how good the bike is. Any suggestions? What do people think about the bikes that Firehouse Bicycles is selling on 50th and Baltimore? I know that they're good mechanics and sell parts are good prices, but I don't know if their bikes are a good price or not. I'm not sure what to look for...

I'm not limiting myself to Firehouse Bicycles; I'm just looking for advice on what to get. Thanks in advance...