My own personal ranking

1. Star Trek III: The Search for Spock

2. Star Trek: The Motion Picture (bet no one excepted this, eh?)

3. Star Trek II: The Wrath of Khan

4. Star Trek VI: The Undiscovered Country

5. Star Trek IV: The Voyage Home (this ranking is tenous, though, as I really need to rewatch the film)

6. Star Trek V: The Final Frontier

7. Star Trek: First Contact

8: Star Trek: Generations

9 Star Trek: Insurrection

10. Star Trek: Nemesis

Haven't seen either of the Bizarro Trek films - and never will - but I would probably rate them far beneath Nemesis if I ever were to.