You want to keep your noggin toasty in the nasty winter weather.
You don't want to wear a hat that looks like everyone else's hat.
You like lions (or dragons).

Now you can combine all of these desires into a simple, yet useful, item of clothing that's infintely customizable and tailorable to your (or a recipient's) tastes.

Disclaimer/apology: Since there's no limit to the variation on this theme, I've only provided the most basic directions. If you have specific questions on how I did certain things, I will be happy to try and explain it in a seperate instructable or through private correspondance.

Step 1: Preliminary Measurements and Layout

You will need:
Fleece
Sewing machine + standard sewing stuff
Scissors, measuring tape
Felt, buttons, etc for finishing touches

Think about what you want to make.

i.e. The lion hat needs a mane and a muzzle, in addition to eyes, nose and ears. I made the mane and muzzle from felt, since I did not wish to deal with unhemmed edges exposed on the outside of the hat.

Measure your head and add half-an-inch: this will be the length of your fleece. The height of the cloth will need to be 9-10 inches, for an adult.

Cut fleece.

Make ears, tails, spines, et cetera:
Sew your idea on to two pieces of fleece (or one piece folded in half), trim it, flip it inside out.
Place these items to the side.

Step 2: Assemble Pieces

Grab the ears you want to add (and if you want a ruff, that too), and any spines or such.

Locate where the pieces want to be (spines go at Center Ridge, ears go at Ears, and ruffs go across Ears as well).

You'll sew the like-color edges together (red edge to red edge, blue to blue.)
Make sure you sew the ears and stuff in place as you sew the edges. You may wish to pin these things in place before you start sewing.

REMEMBER: You are sewing this hat inside out, so please make sure your ears and stuff are placed correctly so that when you finally flip the hat right side out, they'll be in the right place.

Step 3: More Details on Attatching Ears/manes

Here are two photos of my finished lion hat and some clarification (I hope) of how to assemble the mane.

I had first sewn the two seams running from forehead to top-center of the hat, as well as the seam all the way down the back of the hat. This left two seams at the top still unsewn. This is where I put the ears and the mane.

I held the hat right-side-out and figured out how far I wanted the mane and ears to stick up, held it them place between the fabric, and flipped the hat inside-out.
Then I sewed across the entire seam from one side of the hat to the other, pinning down the mane and ears.

Step 4: Finishing Touches

Hopefully your ears and tails and stuff are in the right place.

Have your hat inside-out.
Grab the bottom inch-and-a-half or so of the hat and fold it up, around the "outside".
You're going to hem this thing, so make sure the raw edge is on the inside of the hat, once it all gets flipped right-side out.

Hem with a large zig-zag stitch all around. (This allows the cloth to retain some stretch without tearing the hem-thread.)

Flip your hat right-side out. You're almost done.

Do you need to add a muzzle, eyes, or other facial features to the hat?
Grab your felt. Cut it to shape. Sew it on to the outside of the hat.
Add eyes. A nose. Stuff.

Now trim all the extra thread and stuff, clean up your workspace:
You've got yourself a hat.

Here are some additional ideas:
Cthulhu
Penguin
Dog
Bear
Roman Centurion Helm
Greek Corinthian Helm
Kangaroo
Dragon
Batman
Rooster
Sushi