The Victorinox Classic SD Swiss Army knife is by far the most popular Victorinox knife (about half of the Swiss Army knives left behind in airports are Classic SD models).

The Classic SD is extremely compact and convenient, with five useful tools in a "keychain" size knife that is smaller than your pinkie finger. It deserves its popularity!

Classic SD Camoflage-- camoflage patterns
Classic SD Boy Scout-- adds Boy Scout logo
Classic SD Colors-- a wide range of other colors
Classic SD Retired Colors-- still more colors (retired)
Classic SD Shamrock-- green knife with a shamrock
Classic SD Star of David-- blue knife with a star of David
Classic SD Stayglo-- fluorescent yellow scales
Classic SD Alox-- light aluminum body, no toothpick or tweezers
Classic SD US Army-- black knife with US Army insignia (other services also available)

Ambassador-- similar features in a larger 3 " / 74 mm knife
Bijou SD-- identical features, but no key ring (retired model)
Classic-- identical except for a curved tip on the nail file
Diplomat-- ribbed stainless steel body, no toothpick or tweezers (retired)
Escort-- no scissors
Rally-- adds a bottle opener/combo tool
Signature-- pen instead of toothpick
Stylus-- stylus instead of tweezers
Swisslite-- LED light instead of toothpick

All are slightly larger 2 1/2" (64mm) knives:
Crusader-- no scissors
Esquire-- nail cleaner tip instead of screwdriver tip on nail file
Microlite Esquire-- adds white LED light