I was in your exact same position last year. I found that taking my time worked out well in making this decision.

First of all, take note of the things that make sense to you, both from reading the forums and talking to people at your LBS. I found that anytime I was overwhelmed I just asked more questions until I had no more questions. I also resolved never to make a decision while feeling overwhelmed or overly stimulated.

I think you can walk into a bike shop and know nothing more than you are there to check out bikes. Tell yourself you aren't going to buy one the first time you walk in the shop, so no pressure.

For your commute, you can get away with virtually any bike, which might not help narrow down the choices, but its brings it down to personal choice, which is mostly what people voice on this forum.

There are some popular personal choices expressed on the forum, like planet bike superflash blinkies being the best rear lights. A lot of people like Surly's options (might be more than you want or need to spend at this stage), a lot of people just like steel frames in general (I am one of them), Brooks saddles are also a majority favorite.

My advice is to trust yourself. Trust that you know what is comfortable when you are sitting on a bike and that you are capable of weeding through ****ty sales advice and good, sound, makes-sense advice.

The people on this forum are awesome, so always feel free to post any question and you will get a response. I think we all love helping the proverbial "newbies" because it gives us a chance to reflect back on what we know now and to imagine new possibilities (for bikes that is). It is a process of distilling our knowledge into the most simple 'what works.'

What works in my opinion:

Ride different bikes-for a couple miles each at least.
Work within your budget
Consider used bikes
Acknowledge that loving a bike is a valid reason to buy it (again pay attention to your budget this is where it can get dangerous)
Know that you will tweak your bike over time, most important part of this process is the frame, that's the constant.
Remember that the most important part of riding a bike is having fun! That hasn't changed since you were a kid!

-Bearsong

PS CL stands for craigslist, it took me a while to figure that one out! You might already know that.