Like being frugal? Like being "green"? Crafting on a very limited budget? Finding thread expensive? Yarn supply scarce in your neighborhood? Try reclaiming yarn from used sweaters!
I'm on a very limited budget and thanks to donations and tote purchases, I was able to go to a couple of thrift stores, today, to pick up some sweaters. Here's 9 that I bought:

I'll be reclaiming the yarn from these sweaters. So far, I frogged the purple one and this is what I have so far. This is from a single sleeve!

The sweater yielded 1.5lbs of 100% cotton yarn @ 18 wpi, in a gorgeous shade of purple. I guesstimate that this comes to 1760 yards. I had only 2 oz of waste. For 2.99 and some time, that I would have spent sitting in front of the TV doing nothing anyway, I got yarn that would have cost 6 times a much brand new. How sweet it is!
For detailed information about the process, please visit these pages which have very good instructions and photographs:
http://dawnprickett.blogspot.com/2008/01/recycling-sweaters-for-yarn.html
http://chaoticcrafter.wordpress.com/2008/01/21/reclaiming-yarn-from-a-thrift-store-sweater/
http://cosaverde.com/blog/2010/apr/13/how-reclaim-yarn-sweater/
http://www.craftstylish.com/item/9839/how-to-recycle-yarn-from-a-thrift-store-sweater
I'll be hitting a lot of garage sales this summer too! 
Here's some videos I found which may help:
Here's how I use my chordless drill to make fast work of it:
1) Put a stick in the chuck
2) Wrap the stick with non-skid rubber webbing or similar material
3) Shove a tube or giant spool over the webbing
4) Fold or roll the sweater part so it fits in your hand
5) Tuck the long end under your arm
5) Get the yarn started on the spool
6) Let 'er rip!
(Note: In this video, my battery was just about dead and the drill was not going at full speed. If you think *this* is fast, try it with your drill at full speed!)
