Tours in Milan

We haven't taken a tour, but on different day trips to Milano we have put together a fast-paced (appropriate for the big city!) day tour of our own that we've really enjoyed, running about five hours, on our way from one Italian locale to another through Centrale. Certainly doesn't cover everything there is to see in Milan, but for a whirlwind, it's proven fun!

-At Centrale in the morning, check bags, and purchase two tickets to your next destination later this afternoon (departing about 2:30 PM)
-Take the Metro (yellow line three, dir San Donato) to Piazza Duomo, eat on the 7th floor of the La Rinascente department store, alongside the Duomo (opens at 9:00 AM; great views)
-After breakfast, take the elevator to the roof of the Duomo, the fourth largest church in Europe; also visit the interior (about e9 each for elevator access on either north or south side of church)
-After touring the Duomo, stroll through Galleria Vittorio Emanuelle, browsing and shopping, and through some of the nearby streets (see the world’s most famous opera house, as well: Teatro alla Scala)
-Then hop on Tram No. 16 (catch it just off Piazza Duomo, on the corner of Via Mazzini and Via Dogana; line 24 stopping at Corso Magenta-Santa Maria delle Grazie)- exit Tram at Santa Maria delle Grazie to see Da Vinci's Last Supper (must book a reservation weeks in advance). Get to the church 30 minutes before your appointed time and check in
-Allow about 45 minutes for the visit to The Last Supper (holding room time, 15 minutes of viewing allowed, gift store)
-Have a beverage/snack at the great bar across from Santa Maria della Grazie; return by tram to Piazza Duomo to take the metro back to Centrale (or taxi to Centrale)
-Collect your bags at Centrale, and board your train out of Milano

With more time or an overnight stay, I'd add the Sforza Castle, a nice dinner, and perhaps a live show...and more strolling time in the evening.

To specifically answer your question. A few years ago we did a 4 hour city from the Am Express office. It was good. Second, with the TI, they will also give good information on local tours. That is what we normally do when we are in a city for the first time. Either find the hop on/off bus or find the TI.

Thanks for the replies. I'll consider those options. I was also considering Autostradale or Zani Viaggi.