I've been talking up "My Starbucks Idea" as a great example of how companies can engage their customer base using social media techniques.
The sites about a month old and they are already touting the changes they are making and planning to make in their stores, etc. based on user ideas. The cynic might say these are changes they were going to make anyway and are just making it seem like the customers drove them, but that's not the impression I get.
Check it out.
(Also of note, they built this site on Salesforce.com's force.com -- the newest thing in software development is this idea of platform as a service.)