I'm an odd duck, but I think you should find the lowest costing commuting bike you can find, around $500 is a good range for combination of decent components and reliability. Why do I recommend that? Because about 93% of all people who buy a bike or join a gym, etc quit within 6 months, (this is how gyms can overbook their memberships). Get yourself a nice $500 range bike, then if you decide riding and commuting is not for you then you won't have a $2,000 piece of garage art. If you do decide cycling is your thing then in 2 or 3 years or so you can upgrade to a much nicer bike and still use the old one for commuting and the new one for training rides. Before someone gets off on how unreliable a $500 bike will be it simply is not true. There are people in this world who commute everyday on cheaper Walmart bikes without worry, so I think a $500 LBS bike should last for quite awhile if taken care of.

Don't forget if your commuting and will be parking the bike outside to get a decent lock and not some Walmart lock. Learn how to fix flats in your sleep, I'm not kidding about that. If you arrive to work late too many times due to flats your job could be placed in jeopardy, or they will demand that you take your car. Leave earlier then you think you should in case you do get a flat so you have the time to fix it. There are ways to prevent the majority of flats but nothing is flat proof, and sooner or later it will happen.