I feel a little guilty. While waiting for Congress to decide the royalty-fee fates of beloved Internet-radio services such as Last.fm and Pandora, I discovered newcomer Slacker—and suddenly I'm not so worried about the other guys. Slacker is Web radio done right, combining custom and prefab stations with an elegant interface and top-quality streaming. What's more, the company's business model promises to let the music play on regardless of the new royalty rules, at least according to Slacker reps. That model includes two in-the-works revenue sources:...