Since I have already posted about how to begin a novel, here are some tips/guidelines for ending one on a high note. I am sure that you have all seen the "plot graph" before, but it's a good place to start anyway.
The first thing that I would like to mention about this picture is its deceiving proportions. The 'Resolution' and 'Falling Conflict' part of the line looks pretty big, right? Wrong. Once the CLIMAX happens, you want to get out of there as fast as possible without leaving your reader feeling cheated. The biggest event in your story has already occurred, and all that's left is the cool-down period. One or two scenes/chapters should wrap things up nicely. There is no need to drag the ending on forever. Get in, accomplish what you need to accomplish, and get out, just like clipping the beginnings and ends of scenes.
Another useful tip: unless you feel in your soul that it is absolutely necessary, I strongly advise against killing off your protagonist. Although the death of a hero can be extremely poignant, I recommend adding an 'expendable' sidekick/friend/wizardly guide/someone-likeable that you can redshirt in the final battle (for a Fantasy novel) or kill in some freak accident (for an angsty romance novel). Unless you have a very good reason for doing so, killing off your main character will only succeed in pissing off your readers.
Note: there is an exception to this rule. If you have written a godawful story/novel and want to move on, it is totally acceptable to end it (just for the sake of ending it) by killing all of your mediocre characters in some kind of fire or other natural disaster. Actually, doing this can be rather soothing for your frazzled nerves, and it will allow you to find some closure before moving on to your next project.
If you are writing a romance novel (or any novel with romance in it), for goodness sake, do NOT end the novel with the two main characters on the outs, even if you are planning a sequel so that they can fall back into each other's arms. Have them come together happily at the end. If you want to disrupt the relationship again in your sequel for more drama, feel free, but give the poor person who was kind enough to read your work a bone. Some more romance advice - do not have your characters constantly break up and make up. Once or twice is all right, but if it happens seven or eight times... it gets old. Fictional people in an on-off relationship are just as annoying as friends in real life that don't know when to let it stick or call it quits.
Writing a good ending is a little like cooking a complicated recipe. You want the right amount of left-over tension to make the reader want to buy your other books, but you want to leave the reader with a sense of peace after their journey with you. Do not endeavor to write your ending until you feel that the time is right. Also, you can write your ending WHENEVER the mood strikes, even if your novel is not finished yet. I usually pen my endings long before the middle of the book is finished. I find that they turn out better that way. Like your beginning, you will know when the time is right.