update on feb.15th: i've just release a zine, called do stuff!, which includes a tutorial on the monster hat (with teeth). you can see it here:
http://www.coloredlights.net/leethal/zine/issues/ including the hat pages!
update with more hats and tutorial at the end!!
i didn't mean for that subject to rhyme... oops. anyway, these hats were all made from sweatshirts, sweaters, and t-shirts rescued from various thrift stores. i made them for an upcoming craft show (bazaar bizarre LA woo!) so i would really appreciate feedback about which designs are your favorites, so i can try to whip out somemore before the big day.
i'll write up more details about how they were made if people want, but i think they are pretty self-explanatory... cut a sweatshirt (or whatever) into a box shape if you want ears, or a rounded hat shape if not (but this is harder - ears are eeeasy!), sew it up, and add whatever ya want. with a large sweatshirt, the arm works perfectly, with the bottom of the hat being the part closest to the armpit (of course you will wash it first!) the teeth are made from felt... i don't know what else to add. so, here they are: (small pictures so they load fast, but the bigger versions can be seen on my website -
leethal.net)

sweater sleeve with t-shirt eyes

sweatshirts with crocheted eyes

t-shirts with drawstring tie through the sleeve edge for the top

2 sweaters

sweatshirt with yarn stitching

sweater with buttons and yarn stitching

t-shirt with machine-sewn face

sweatshirt with a sock cut into the snake

sweatshirts and a t-shirt
ok that's all of em, whadya think? thanks for any feedback!!
UPDATE:
ok so the craft show was over awhile ago - it went well! thanks for all the rad feedback, i really appreciate it!!
i made a couple more based on the advice you guys gave me, and limited by the time i had...

2 sweaters

sweaters with yellow t-shirt eyes and a sweatshirt beak
(i also made some matching mitts and other things, but this is a hat post...)
oh, just a note: my descriptions under the pictures are not what i call the hats, they are letting you know what materials i used so you can figure out how to recreate them if you wish to. (my hat names are things like "colorful owl eyes hat" and "bulging eye monster hat")
ok so someone asked for a tutorial for the owl hat, so i made one up for ya. first, here are bigger versions of the pictures so you can better see what it looks like and the tutorial will make more sense (hopefully!)...
you'll need: a large sweater, some scrap fabric in different colors, either a sewing machine or needle+thread, possibly yarn+big needle if you want to hand-stitch like i did, seam ripper, scissors (duh)
the shape of this hat (high on the forehead, long in back) and the little beaky point in the front came from the natural shape of the sweater sleeve when detached at the shoulder seam. (i took the sweater apart planning to cut it into a normal hat shape, but was happily surprised at the unique shape i'd discovered.) if your sweater won't come apart neatly, you can sew around to keep it from unraveling, but hopefully you'll be lucky like i was and won't have to.
ok i hope that all makes sense, let me know if something is confusing...
i think that was probably the least self-explanatory of all the hats, but if you really want a tutorial for another one i'll try to post one. (i am actually starting a zine that will have some how-to's for hats and other things, i plan to release the first issue february 1st if you're interested...)
thanks again for all the great comments and i'm soo glad to be inspiring so many crafters to make their own wacky hats!!!!!!