It seems like a lot of writers are worried about the lengths of their chapters. What's considered too long, too short? What's just-right?
The good thing here is that the answer is short and sweet: there is no ideal chapter length. As long as all of your chapters are reasonably consistent (i.e. don't have one chapter take fifty pages and another take five), you'll be just fine.
Some books, like Maximum Ride, for example, have very short chapters. Many of these chapters have two to four pages. I've heard that Stephen King wrote a chapter that had only four words. Having short chapters like this makes the story seem like it moves along more quickly, highlighting the feelings of action and suspense. Some books, on the other hand, could have chapters up to fifty pages in length. This is fine, too. It highlights the complexity of the story, and breaks it up into broad pieces that each have something a little different.
The one thing to remember with chapters is that you never want to end in safe place. When you're reading a book, you want a convenient place to put it down, right? You're not going to stop reading in the middle of an action sequence or when something important is about to be revealed. You want to put it down in a place that's comfortable and has little or no tension.
Because of this, you don't want to end your chapter in a "safe" spot. Don't end with the protagonist contemplating recent events before she turns out the light to go to sleep. Instead, end with your main character dangling off the edge of a cliff. If you end every chapter with a moment of suspense, readers won't want to put your book down.
Edit (8/9/11): "Safe" doesn't necessarily mean that the MC is safe from space aliens or whatever. The character could be physically safe, but maybe the chapter ends with the revelation that the captain of the space aliens is actually her ex-boyfriend, or something. And action doesn't have to be life-threatening, either. It could also mean a heated argument, a love scene, etc.
Just remember: when you write a book, your goal is to write something that your readers can't put down. If you end each chapter with something exciting, they'll want to stay up half the night saying "one more chapter...one more chapter..."