Lost another bag during travel? That stinks. Since bags don't come with a GPS radio (at least, I haven't seen one yet), here's the next best solution: the Garmin GTU-10, an always-connected dongle.
Drop the tiny gadget in your briefcase, for instance, and get access to its location 24/7. Equipped with GPS, cellular and GSM radios, the tiny fob will allow you to quickly ascertain whether you accidentally left that briefcase in the hotel, the taxi or the restaurant (oh heck, it's the strip club). Yes, you can use it to spy on people's location, too, but it's a tad too big to be all that discreet (you seriously can't expect someone not to notice a dongle slipped into their pants pocket).
The Garmin GTU-10 measures 3 inches and weighs 1.7 ounces. Sure, that's not nearly as impressive as those minuscule homing devices they use in the movies, but you're not a super spy either, so this should get the job done adequately. The entire dongle is waterproof, so accidentally dropping your bag in the river won't cause any problems finding it (recovering the bag, however, is another story). A full charge keeps it sending signals up to four weeks (minimum operational mode) -- enough time to do everything in your power to get it back.
Tracking, which will show the signal source on a map, can be done on demand over both computers and smartphones (the latter, via an app). It's got a ton of extra features too, including setting up virtual checkpoints (emails and SMS are automatically sent) and history tracking.
Amazon has the Garmin GTU-10, priced at around $222.