Hmm, The Old Guard at Waterloo deserves a look by the thread's starter, as well as the Battle of the Alamo. If we're going to concentrate on the American continents then I'd be an idiot to omit The Battle of Camerone (that famous day in French Foreign Legion history!). I suppose the Battle of Little Big Horn would also fit the criteria, but that an ending that may not be 100% what the OP's looking for. Rorke's Drift has been mentioned, but not Isandhlwana interestingly enough. Can't forget Rorke's Drift raison d'être, can we?
Moving to a more contemporary era, the World War II defense of Wake Atoll deserves a look over. Equally, the defense of Betio Island and Tarawa Atoll merit a once-over (also, Corridor). The Americans also did a smashing job with the defense of Bastogne and the famous reply "Nuts" sparks the imagination.
Last, but certainly not least, is the defense of the Arnhem Bridge. It was made into a smashing movie "A Bridge to Far" (which I suggest everyone watch) and has become ingrained into American culture better than any other contemporary battle. It's definitely one of the best examples wanted by the topic thread.