There's a very good article in today's NYT about finding traditional Lombard cuisine in Milan along with a general guide to the city. Here's the link:
My personal experience with these places is limited except for Trattoria Milanese. That place is a classic institution and pretty much in the heart of the city. Run, don't walk.
Bebel's is right near my apartment but a few things have put me off. 1) The first time I went there it was full and we couldn't get a table. It seemed pretty clubby and filled with the hoi polloi. It's obviously not the neighborhood place that it seems to be from the street. 2) While you probably wouldn't order a pizza here, they cost 10 euros which is a little steep, secondo me. In other words, I'm skeptical about the quality/price ratio. (maybe I'm just cheap)
Of course, this has nothing to do with the food.
The other place, Trattoria della Pesa is a bit away from the center of the city. I've walked by it a few times and it has always looked good. I'm definitely saving my pennies to try it out.
Lastly, here's a link to Il Mangelo which publishes a guide to restaurants in Milan and Rome. If you register, you get more search capabilities. I find it interesting because its contributions are from regular Italians. What I've found is that its recommendations for Italian food are usually spot on but if you want ethnic food, I wouldn't trust it so much. http://www.ilmangelo.it/