Altec Lansing’s inMotion iM3 is styled for an iPod but works with any digital music player. Good thing, too, because it folds to paperback-size for travel and produces pleasant — if a little wimpy — sound. $180. www.alteclansing.com

Sonic Impact Technologies SI-5 Gen3 speakers add surround sound to the previous generation’s mix of small size plus built-in amplification. They still weigh in at less than a pound, and at $59, are cheap enough to be a guilt-free addition to your roll-aboard. www.si-5.com
— T.S.