My favorite pattern to do with scraps of yarn is make a "celebrity" scarf (like the ones that Jennifer Aniston and Jessica Simpson wear). I use 5 different yarns, normally with at least one novelty yarn like Fun Fur or Boa.
I use a 9 or a size needle that makes a nice fabric with the yarns I have and cast on about 6-8 stitches with the first color. I knit in garter stitch for about 20-25 rows, then add the next yarn and do the same for all 5 yarns. Then I add nice long fringe to the end combining all the yarn used.
Normally the scarf ends up being about 6 feet long or so with 10" of fringe on each side. Teenagers love them, so I normally give them to my niece and her friends as gifts.
The best part is I can get 2 or 3 scarf sections out of about 80 yards of novelty yarn, so I can make a bunch with just a few skeins.
What a great idea I have a stash of left overs that I just cant throw away but had until today no idea what to do with except maybe to knit a stripe in a sweater but a scarf of many clors Wow what a great idea