(edited on 11/24/11 to add: I found this random number generator to help you pick a number. It even allows you to set it for any upper and lower limit.)
1- Your characters meet a random dog. They try to read the tag, but it keeps wiggling away.
2- Something explodes in the sky above them.
3- Your main character sits down and contemplates how he/she's divided. He/she really wants that main goal, but must have to give up something to get it. Go deep with this one. Put soul into the scene, not explosions. I believe it was Orson Scott Card who once wrote that thought is action.
4- A character smells something strange. Describe it in detail.
5- A character goes blind.
6- Something explodes.
7- Somebody spills something. How do they feel about it? How do others react?
8-A character tastes something new. Describe it in detail.
9-They find a dead animal.
10-Put music in your story- somebody sings or an instrument.
11-Your character realizes she/he lost a favorite necklace or pocketwatch.
12- He/she sits down to read and finds parallels in the story with his own life.
13- Write from another point of view. Just try it and see. Even if it's not in the final novel, it's eye-opening for you.
14- Your character prays.
15- Somebody gets drunk. What are the ramifications?
16- A man in a hat and umbrella is watching your characters from afar. Just put it in, even if it seems out of place. Trust me on this. :)
17- Somebody thinks your character lied when they haven't.
18- Look to your right, left and center. Write down three things you see. Now write a scene involving those objects. No cheating. If they can't possibly be in your novel, somebody can imagine/remember them.
19- Compose a poem about your character or novel. (I actually did this and one of my characters sings the song in the novel.)
20- A baby monkey riding backwards on a pig go by. How do your characters feel about it?
21- Write a chapter with no dialogue.
22- Your character must go shopping for bread.
23- Somebody suspects they're pregnant. How does everyone respond?
24- A large dog is hiding behind a house.
25- Somebody finds a gun in a drawer.
26- It rains. Does your character like rain? Describe the experience in detail.
27- The most unlikely character in the novel dances.
28- Write a chapter with only dialogue.
29- Write a chapter that begins- "I've lost my suspenders."
30- The weather unexpectedly changes and your characters are unprepared.
31- Write the closing scene to your novel if you haven't already. Do it now even though you haven't written the rest. You'll know where you're headed and you can always modify it later.
32- Hundreds of butterflies are suddenly flocking toward your characters. What now?
33- Write a gambling scene.
34- Open a scene with the words, "The stench was unbearable."
35- Write a journal entry or letter written by your character- main character or any character you're trying to get to know.
36- Give the villain, or some unsympathetic character, a stomachache and have to curl up in the fetal position for a while.
37- There's a car crash, steambike crash, space vehicle, or horse and carriage crash (depending on your genre).
38- Somebody says, "Hasn't this all happened before?" Everyone looks at him and he says, "Never mind. Déjà vu." Dumb, but it's a NaNoWriMo filler until you think of the right dialogue.
39- They find a dead kitten. The toughest guy cries.
40- Somebody makes a Shakespeare reference and after that, eerily the story starts to take on the shape of Macbeth.
41- A new character is introduced. He/she resembles your real life first grade teacher.
42- The TARDIS appears, Doctor Who steps out, and ...