I'm new to bike commuting too. I bought my bike about 6 weeks ago, just before I heard of this site. I first went to friends that I know that ride and asked them, and looked around online, and I got advice that was all over the map. I finally went to REI in Seattle, and narrowed it down by category and price there, and went with that. (Not saying you should, just saying that's what I did.) I wound up buying their Novara Forza, which is a hybrid - flat handlebars, large diameter wheels, but wide, treaded tires. My commute has some rough spots, and Seattle averages 288 days a year of rain. So far I like it a lot. It's just the thing for me for bombing around town on, through parks and to work, errands, etc. I'm on it more than I expected. I'm already thinking about eventually getting a road bike for longer trips and weekend tours. (Like I said, I have friends that ride.) But I'm sure I'll still use this one as the urban assault bike and commuter.
Take your time and keep looking. You might see something and say "That's IT!" I sort of found this one that way. I am by no means an expert on bikes, but after looking around, I picked out this Forza and am really happy with it.
Good luck!