I liked the Alien bunch with the exception of the prison planet one. It was kind of a dud. As far as B movies go, the flesh eating zombie ones are pretty good (quite funny).
I didn't like Stars Wars as much as LOTR and Harry Potter movies. I think it's ridiculous that people classify Star Wars as being Science Fiction. To me it's more fantasy than anything, so it belongs in the same genre as LOTR and Harry Potter, IMO.
Back to the Future was pretty good, too. And I liked the X-men movies. Also, Underworld, Ice Age, the French Connection, Final Destination, Shrek, The Man with No Name trilogy (Fistfull Of Dollars, etc.), Croc Dundee, Rush Hour, Samurai, Resident Evil, Home Alone, the Jason Bourne movies, The Naked Gun, Mad Max, etc.