my recommended 5 star hotel are:
1. Boscolo Hotel
2. Armani Hotel
3. TownHouse Duomo
4. Magna Pars Suites
I suggest this hotel for people who are looking for spacious room, but it is bit far from Milan city center.
In Milan, there are much higher end hotels than my recommended list, but it is not worth it, unless you want spoil yourself to luxury.
For economical travelers, I recommend Crown Plaza Milan, because metro sub station is just 5 meter away from hotel door, and this sub station is just 2 station away from Milan city center.
In conclusion, there are limitless of choices for accommodations that suits every necessity and budget within Milan city center, and you can browse for information and pictures of hotels in Milan by going to Booking.com or Kayak.com