I liked the opening credits for the Blackhole and battlestar galactica. Raiders of the lost ark is my favorite movie as the opening scene just sets the tone for the movie and grabs you from the start
I quite liked Fight Club. And the credits sequence to Watchmen was amazing too...sometimes I'll just watch the credits and turn it off.
There was an absolutely unwatchable movie about ten years ago called "Enter the Void" (I'm sure Snikt thought it was "brilliant") that had a truly amazing opening credit sequence.
Star Wars and Raiders probably have the #1 and #2 best openings of all films but they don't really have compartmentalized opening credit sequences per se.
If you go by *only* the opening credits themselves then Conan the Barbarian is my favorite. I literally get chills every single time.
After that I'd probably say The Terminator. T2 was very good as well. They really knew how to open an Arnold film back in the day.
I agree with most of the previous mentions but I'll go a little different route. For me a real good one was Red Dragon because it showed for the 1st time how Will figured out Hannibal was the guy he was looking for. The answer was right there in front of him but he didn't see it. Hannibal showing his true self and the struggle for Will to survive was cool to finally see on film. I always tune in to the opening of RD then hop in and out of the rest of the film.