Soviet paratroopers landing on a high school football field is everyone's biggst fear, so Red Dawn is easily the best of this genre. I will forever join my fellow patriots in shouting "WOLVERIIIIIIIIIIIIIIINES!!!!!" and let us not forget that one guy wearing a crusty Star Wars hat.
Invasion USA was pretty good, too. Not Chuck Norris' best movie but that's not a slight against IUSA since Charles makes some good ones.