I have been on a quest to find the best Italian Beef Sandwich in Phoenix. I have been all over this valley and have eaten many a sandwich claiming to be Italian Beef. I won't hold you in suspense any longer:

Lukes of Chicago

You may not know it but the bun is crucial to a succsessful Italian Beef Sandwich.  A good one is almost dripping with juice, and of course the bread absorbs a lot of it.  The bun needs to hold together under this assault from the juice.  Most buns simply disintegrate.  Luke's understands this and uses a bun that is soft but chewy and the glutens hold it together.

The beef is tasty with a touch of spiciness – probably to accomodate our southwestern tastebuds.