The title of this thread speaks for itself. I have only included movies in which Arnold is the star or play a major part. As such, there's no The Expendables (only the sequel) or Around the World in 80 Days for example.
My favorite is Commando. It has everything that makes a Schwarzenegger movie great. Over the top action, inhuman feats, guns and knives in abundance, an impressive body count and last, but not least, a memorable villain. Commando would not have been the same had it not been for this Freddie Mercury look-alike, knife wielding, chainmail wearing psychopath known as Bennett.