General guidelines for learning stroke order
The best place to start is with the Wikipedia entry on stroke order. It lists these guidelines, along with more detail and some nice animated examples:


  
  Write from top to bottom, and left to right. 
  Horizontal before vertical 
  Diagonals right-to-left before diagonals left-to-right 
  Center before outside in vertically symmetrical characters 
  Enclosures before contents 
  Left vertical before enclosing 
  Bottom enclosures last 
  Dots and minor strokes last 
  


In my experience, you don't need to panic about the details of each character, and there is sometimes disagreement about the "correct" order. If you learn the general guidelines, you won't usually make embarrassing mistakes. If you do want to see the details of a specific character, there are lots of on-line resources. Here are the two I most often use:


MDBG.net - Type the pinyin and press enter, then click on the character you want. Finally, hover over the >> arrow and click on the brush to see a stroke order animation.
zhongwen.com - Use the search page to find the character you want, then scroll to the bottom and click on the "Animated" link to see a different stroke order animation.


Although those are the two I use most often, the stroke order reference I find most beautiful and readable is the Wikimedia Commons Stroke Order Project, specifically, the Black and White images. Here's an example:



They're much easier for me to use than an animation, because they are static images. I can scan back and forth with my eye, instead of waiting for the animation to cycle through. I used them as the inspiration for my Mnemosyne flash card files. Mine aren't quite as pretty, because they are automatically generated, but they have the added feature of a grid to guide your stroke placement.

I just discovered the Stroke Fanning reference. It's very compact (500 characters on a two-page PDF), but I still find the Wikimedia Commons format much more intuitive to read.