Beyond EXIF, there's also IPTC, which the afore-mentioned Lightroom is pretty good at managing. Couple that with built in geo-tagging of photos thanks to camera

Beyond EXIF, there's also IPTC, which the afore-mentioned Lightroom is pretty good at managing. Couple that with built in geo-tagging of photos thanks to cameras with built in GPS (or do it after the fact with a GPS logger) and you can have a pretty decent system. Both the geographic feature and the keyword feature allow for hierarchies, not just strictly free tagging.