Perhaps this belongs in the Xtreme Consumer Reports thread, but I figured it was time for a new thread anyway.

I'll start things off with a personal example: just got done internet-chatting with a Charter Communications rep whose job was to keep my business. Our 6 month promotional period was coming to a close, and our cable/internet bill was going to go up by $30 next month. All I had to do was ask about cheaper alternatives, and she ended up offering me the exact same promotion for another 12 months. hooray for saving $360! (In reality, if she hadn't offered me the promotion, I would have looked for other alternatives like downgrading my internet speed.. but as it turns out I didn't have to!)
I did the same thing with AT&T a while back and scored free high-def service for a year plus $15/month off internet just for asking. Generally if you're not under contract with a company, just mentioning the possibility of switching is enough to get them to offer a better deal.