Let's try a superhero themed animation using free online sources to build your characters, creative commons images for interactions, and copyright free music all animated in Keynote.

Let's watch a couple examples first:

Everybody can be a superhero. Think of your interests, talents, knowledge then exaggerate it. That's all it takes.
Think of how you can use this for GOOD (not evil-that's the key). So let's say you're great at making scrabbled eggs.
Then turn that into a superhero power with a name that fits, ie "The Scrambler" with a slogan "like able to make the bad guys scram!"
Let's start by building your avatars.
1. You need the everyday or "Clark Kent" version of yourself
Try building that at Mad men yourself
If you add things to hold in your hand, make sure you incorporate that into your storyline.
Choose a blank white(last choice on the projector) so we can use instant alpha to erase it later.
Download the SCENE version, standard size is fine.
If you get tired of the audio, click the speaker icon in the lower right corner.

2. Open your mad men avatar in PREVIEW by double clicking on the image download. Use the crop tool to select a tight rectangle around your image (apple K is crop). Save this for later.

3. Now, build your superhero version of yourself using the hero machine.

You don't have to add anything to your hands unless that is part of the storyline.
Take a selected screen shot of the entire avatar by using the "command" Shift 4 keys,
dragging the crosshairs over the avatar and some background, then letting go.
You'll find your image on the desktop. We're going to need to erase the background later.

kitchen.jpg4. Now let's find a setting for your animation.
Here is a link to Flickr landscapes with a creative commons license.
Don't use a copyrighted image in your animation.
If a landscape doesn't work for you, type in a different keyword into the search box.
I tried "Kitchen" since that made sense for the Scrambler.
Find a nice size (horizontal is best) image, choose "actions",
view all sizes and download the biggest size you can.
Do you need any other images to tell your story?
I might need a frying pan.
external image 5023480824_d5c1feab03_m.jpg

5. Now, have you thought about your script? It might help to make the animation first then think about what you want to say next.
Let's open up Keynote (it might be in you iWorks folder in Applications unless you bought it from the Mac App store-then it's in your dock).
Set up a blank slideshow. Layer in your setting image in the background. Make it fill the entire space. It can even be too big-that extra won't show. Click the play button to test. Now, find your "Clark Kent" avatar. Drag that image onto your slide.

6. Make your avatar have a transparent background. We can do this in Keynote using the instant alpha button. Select the image, click Instant Alpha from the menu, click and drag into the background until it seems selected. Be careful that you don't erase part of your avatar (if so, click UNDO or apple Z). When you're happy, click outside the image area. If you see a spot you missed, do the same steps to erase more. I added a frying pan image to mine, so before I animate I need to select both images and group them so that they move together. This is optional. You could have the objects move individually.
Watch this screencast to see steps 5 and 6.
Or watch it below:
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7. Now I'm ready to make the slide for my superhero avatar. I could chose the + button or select the whole slide on the left side under where it says, Slides. It will get a yellow edge when selected. Then choose "duplicate slide" (or apple D). I'll select my "Clark Kent" avatar and the hit delete key. Then I'll drop in my super hero avatar, erase the background with instant alpha again, and resize her. See step 7 in this screencast or watch it below.
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8. Time to write your script. I like to take notes in the "presenter notes" area under my slides (find that option in the menu). These words never show, but they help you organize your thoughts and you can later read it like a script when you record yourself.
9. When you're done writing you're ready to record. I decided to make the first two slides a narration (where only my audio will be needed) and then I added a third slide with a close up of my superhero. I'm going to need video/audio for this slide. So, I'll open up photo booth and use my built in mic and iSight camera to make my three recordings. I know I said I only need audio for the first two, but I'll record the video anyway and hide the video behind my background image in my slide.
Watch how this works in this screencast here or watch below:
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10. Let's go find some music to drop in. Use and click on a descriptive word like "Adventure/Action". Find a piece of music that is about 10 seconds long so you won't have to edit. When you click on it, it will download and play in itunes. An easy way to grab the file is to click once on file in the download window, hold down the control key and choose "show in finder". Then grab the file and drag it into you keynote slide.
11. Time to animate!
First decide how you want to move in your "Clark Kent" character into your scene. Does he/she move in from the left/right/top/bottom of the screen?
There are so many possibilities. He could dissolve in, flip in, shimmer in, etc... take a look at the inspector's build options and play.
Here are the steps I went through to animate my first slide in this screencast or watch below.
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12. Now it's time to set all the animations and slide transitions. You need slide transitions to be practice playing your animation and calculate how long each slide needs before it should automatically transition to the next slide. When you have everything ready, play back your animation and see if it flows nicely. If so, you're ready to export your animation to a quicktime file. Chose fixed timings and set it to One second, One second. Take a look at what I mean here in this screencast or watch below:
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Watch my final quicktime animation here:

I usually refine my keynote animations in iMovie. I trim down the pauses between slide transitions
and add a nice theme with titles and credits like my finished example above.