Good Italian textbook with a focus on conversation. It's a bit hard at first as new words are introduced out of nowhere. It forces you to learn them, which is good, but it also creates roadblocks in getting through the material as efficiently as one potentially should. That said, this textbook is my new best friend. I reread it constantly and find myself always learning more.
UPDATE 11/7/11:
After purchasing and reading Prego! 6th edition, I have to update my review for Parliamo Italiano. Prego! is much better in allowing the reader to go through as it provides translations on-page in the footer, so you don't have to rush off to a dictionary and spend additional time looking it up. Prego! also has a glossary that's usable. I had a game with Parliamo Italiano: If I looked up a word in their glossary (even words used in the very same book), I would bet that I wouldn't find it. Usually, I would win. This is very sad and annoying.
In terms of design, dialogue and the amount you can ultimately get out of it, I like Parliamo Italiano more. In terms of usability, Prego! is much more stress-free. You don't want a frustrating read to prevent you from picking up the book.