I sometimes borrow my wife's road bike. It is not optimum for my commute, but it works fine. Since you are planning to get a new bike, I would suggest just buying a battery light (Road Toad, or equivalent), rear blinkie, and a backpack for stuff. Fenders would be good if you can fit them. You may want to get more puncture resistant tires and fit Tuffies. The idea is to set it up to make it a bit more suitable for commuting for now and so it can serve as your weekend bike/backup when you get another one.

What you should get for commuting depends upon a lot of things, including trip length, type of clothing to be worn while riding, the extent to which you don't mind doing maintenance, and how secure your parking area is. I think it is a "horses for courses" sort of thing -- what works for me may not work for you and vice versa. When I went shopping for my bike, I considered the following items to be requirements:

Internal gears
Chainguard
Disk or drum brakes
Dynamo lighting
Fenders
Rack

This if for a ten mile, all weather, year-round commute, mostly in urban traffic with many stoplights in a moderately hilly area near DC. There is one half mile stretch where I can get down in the drops and whiz when I am on the road bike, but it is less suited to the rest of the course. You will have to figure out what your own needs are, based on your riding plans.

Paul