I'm a size 8.½ and have a vaguely narrow-to-medium foot. This sock fits me great, and I love it. Koigu is a standard sock-weight yarn that can be purchased at http://www.patternworks.com/. It's a bit pricey, though; I sort of splurged for myself when I got it. It's merino, so it's nice and soft. I recommend knitting in a strand of #20 crochet cotton in the toe for reinforcement.
Lately, I've found myself altering this pattern slightly. I've been continuing the ribbing over the instep and doing a 50-rnd cuff instead of the 35-rnd one specified in the pattern. The ribbed instep just fits very well and feels great, and the longer ribbing is nice to tuck under your jeans (or fold over if you wish).
Materials:
Cast 24 stitches on each of three dpn's for a total of 72 stitches. Knit 35 rounds of k2-p2 ribbing, 50 rnds if you like a longer cuff.
Knit the next 18 stitches and slip them to the first dpn. Rearrange the stitches such that there are 36 on the first dpn, and 18 each on the other two.
WS: Slip the first stitch only, then p across. RS: (S1, k1) across. Repeat these two rows 18 times total across 36 heel stitches. Leave the two instep needles untouched.
WS: S1, p22, p2tog, p1. Turn.
RS: S1, k11, ssk, k1. Turn.
WS: S1, p12, p2tog, p1. Turn.
RS: S1, k13, ssk, k1. Turn.
Continue in this vein, working one more stitch each row before turning until
you've finished up with a RS row and have 24 stitches on the heel needle.
Pick up 20 stitches along the side of the heel flap and slip them to the first needle. Knit the stitches from the next two needles onto the second needle. Maintain the ribbing pattern over these two needles if you want the ribbing to continue over your instep. Pick up 20 stitches from the other side of the heel flap onto the third needle and knit 12 heel stitches onto this needle. The round now begins in the center of the heel. 100 stitches.
First round: Knit along the first needle to the last three stitches. K2tog, k1. Knit across the second needle, maintaining ribbing pattern if desired. On third needle, k1, ssk, k across. Second round: Knit even, maintaining ribbing over instep if desired.
Repeat these two rounds until you're back to 18 stitches on the first and third needle, 36 on the second.
Knit around even until you are at the first knuckle of your big toe (the one where bunions form). That's 27 rounds for me, and I wear a size 8½. Maintain ribbing over instep if desired.
First round, first needle: Knit to last 3 stitches, then k2tog, k1. Second needle: k1, ssk, k across to last 3 stitches, k2tog, k1. Third needle: k1, ssk, k to end. Second round: knit even. FWIW, I've never continued the ribbing over the toe.
Repeat these two rounds until 22 stitches remain on the second needle. Knit the first round three times with no even round between until 16 stitches remain on second needle. Knit the 8 stitches on the first needle and slip them to the third. Cut the yarn and leave about a foot or so of it hanging to graft the stitches closed.
There's a fantastic page up at http://www.pcola.gulf.net/~enp/sockpage/lessons/lessons.html that has great directions and pictures showing each step to grafting stitches together. Follow these directions and your sock-toes will be the envy of all who witness your feet.