I crocheted mine, only I did them in the round. I absolutely love the way they turned out. I didn't really follow any particular color pattern, just changing colors on rows at whim, but they turned out so very cool. The really neat thing is how well they work, too.
I keep one at my computer desk for my coffee. I made it a little larger than normal, as I drink out of an oversized mug. I made the others normal sized for tea glasses, and they really do absorb the moisture.
I used tapestry wool for mine. I found several skeins at Salvation Army for about 20 cents a skein. They were very 70'ish colors, and my ds's girlfriend told me my coasters look very "retro".