I thought of a couple more that haven't been mentioned yet:

A Shot in the Dark
From Russia With Love

Death Wish II

Some of you are right, but most of you are wrong, dead wrong, about the sequels being better than the original.

Note 1: The question is not, "Hey! What are some pretty good sequels?" The question is: what sequels are better than the original film? As good as Toy Story 2 was, it was not better than the original. Similarly, Psycho II was not a terrible movie, but Psycho was a classic. Other examples of this that have been mentioned:

Indiana Jones and the Last Crusade
Die Hard 2
Addams Family Values
any of the James Bond films mentioned (better than Dr. No?)

Note 2: Some of you are, for lack of a better word, clearly bat-sh't insane. Batman Forever? Speed 2 You do understand the difference between a good movie and a bad movie, right? I mean, Rush Hour 2? You have actually seen a movie, yes? Multiple still images... combined together to create... the illusion of motion... does any of this ring a bell? Anything? Hello? The Mummy Returns, people? People?

Note 3: OK, there are some sequels that are better than the original. Better in the sense of quality of script, of direction, of plot. Yes, Empire is better than Star Wars and Godfather II beats the original Godfather for exactly these reasons -- the storylines are more sophisticated, the characters are given more of a chance to grow, etc. While I agree with Pants's point about the first movie laying the foundation for subsequent films... I think if you just compare the original movie to the sequel on it's own merits, a film like The Bride of Frankenstein is better on most counts. (IMO)

Just so my opinions are made clear:

Toy Story 2 is better than Toy Story (not by a lot, but it is better)
Addams Family Values is better than The Addams Family...by a HUGE margain.
From Russia With Love, Goldfinger, and several other Bond films are better than Dr. No.

I really have nothing new to add, but I'll give my to

Bride of Frankenstein
Bill & Ted's Bogus Journey
Godfather Pt.II
Evil Dead II
Dawn of the Dead
Drunken Master II
Batman Returns
Empire Strikes Back

Aliens isn't BETTER than Alien, but it's just as good in a completely different way.

And Groucho beat me to 'A Shot in the Dark'!

Terminator 2
Austin Powers - The Spy Who Shagged Me
Harry Potter and the Chamber of Secrets
Godfather 2

Nothing original, but still.

Those of you saying you think T1 is better than T2 PLEASE expand on why you actually believe this. It's puzzling to say the least...

Don't forget Jason X2

T2 and Toy Story 2.

There's this new thing I've discovered! It's called an opinion.

I want to add the "Hulk 2" to the list.

I know it hasn't come out yet, but there is no way it can be worse.

You're wrong!

That's your opinion!

Wrong again, buddy!

Eddie and the Cruisers 2: Eddie Lives

Spy Kids 2
Dumb and Dumberer
Stuart Little 2
Friday the 13th Part2
Halloween Part 2 Season of the Witch
The Texas Chainsaw Massacre 2

NNNNNOOOOOOOOOOOOOOOTTTTTTTTTTTTTTTTTTTTTT!

Lethal Weapon 2