Apple iPhone users can tag their photos with GPS location using the gps4cam application. This applies not just to iPhone photos but photographs taken from any digital camera. The iPhone GPS is used to provide location data at a customizable interval whicha is encoded in a special QR code shown on the iPhone. Accompanying PC or Mac software decodes the QR code and applies location data to all the photos from the trip.
This lets you add this functionality to your existing iPhone rather than buy a dedicated device which you must carry and charge separately from your iPhone. The gps4cam software support less precises economic mode to avoid running down your iPhone battery on longer trips.
The gps4cam iPhone application is available for $1.99 USD from the Apple App Store.