Hi I tend to favor old mnt bikes for commuting. They are high quality but you can score they for cheap on Craigslist. Craiglist is excellent in your part of the country. I need 2 bikes for my commute and bought a Spec. Stumjumper mid 80's, deore comps for 70.00, and a Gary Fisher 80.00. I've used these bikes for the last 4 years commuting in kinds of crap weather and they keep on ticking. I just rebuilt the GF as it is the one that gets the most mileage. The bikes together have about 12,000 miles in the last four years. I wouldn't buy a new shiny model as it will attract thieves and you'll worry about rain/snow/salt.... Here's one for cheap:
http://portland.craigslist.org/bik/100871292.html
Things too keep in mind, clearance for fenders(this is easy if you go to skinnier slicks) and eyelets to attach fenders and a rack(unless you use backpack).