Yea, you can do a search and find a million threads on commuter bike selection. But if you tell us how much you're willing to spend on a bike we'd be happy to make a few suggestions. It's good that you've already been reading up on various bikes. You should take all the knowledge you can when shopping. You will probably know more about bikes than a few salespeople.
And a few things are crucial. Like, is this really going to replace your car during the week? That would be excellent, and you might want to spend a little more if that is indeed the case. Also; tell us more about your shortest route. Is it flat or hilly? Is the pavement nice all the way? Or do you have to deal with bad roads or dirt paths? What's the weather like where you are?
Also consider whether or not you can store your bike inside the workplace during the day, or if you will be locking it up outside. If you have to lock it up outside you might consider a second hand beater, as it will be less attractive to thieves. I'm not talking about a worn out bike that might leave you stranded. But a used one, with some obvious wear and tear on the frame, that is mechanically refurbished so that it will be reliable daily transportation. Depending on your budget, that might be the best choice anyway.
I used to ride 30 miles to work on my single speed Surly Crosscheck cyclocross bike. The route included a few really decent hills and took me two hours in the morning. However, I only road it one way, two or three times a week. If I was feeling froggy, I'd take the bike on the train half way home and ride the rest. Now I have a nine mile commute and can ride both ways evey day if I'm not being lazy. If I ride my Crosscheck, I take it inside during the day. However, I do have a beater as well. It's an old ridgid mountain bike with 1.5" wide street slicks and just 9 speeds - one ring in the front, nine cogs in the back. Then again, when you're used to just one speed, nine is alot! It's very convenient to just throw a cable on the beater outside and stroll into work.
If you're going to be riding mostly flat terrain consider a single speed for your daily ride. It will really cut down on maintenance. You won't find many light weight, single speed commuters in bike shops though. But all the help you need for putting one together is over on the fixed gear/ single speed section of this forum.
Hope this helps. DanO