I'll go along with others advising a used bike as a better value, they don't have to be $25 beaters even though my $25 bike was able to take me to work every day. Even then if I wasn't able to take my bike into work with me I would have taken a cheaper one. When getting a new bike it is also important that you find a good bike shop to do business with.

One advantage of bikes is that having two isn't like having two cars, and if you are reasonably handy you can tackle alot of the mechanical things required to keep your bike going, which is always a good idea for a commuter. So a spare bike would be good insurance to keep you on two wheels should a silly part break or you are too lazy/busy to fix something immediately.

It's free to read all the info here as well as blogs and whatnot elsewhere on the net and you'll be able to come to your own conclusion, rather than everyone elses, since rarely will you see advice from an individual that differs from there own path.

good luck