Here in the Veneto, the former Republic of Venice, the dialect is still very alive and well, and in many situations is more prevalent than Italian. And it really is quite different than Italian in many ways:

"She's a beautiful girl"

Italian: E` una bella ragazza.

Venetian Dialect (at least one version of it): Xe na bea tosa.

Lots of words change, and even the grammar a bit. Indeed, with many italian "dialects" it's quite likely that they evolved from Latin on their own, rather than there being some standard "Italian" that then diverged.

It's really amazing, too, how much it changes over short distances - I can't hear it myself, I don't speak it that well, but you can ride an hour by bicycle from here and people recognize that you're from over there...

Edit: another good bit of dialect would be appropriate for the comment by Mark_Book below, "xe un mona".