Take your socks.
Make sure they're ankle socks, ie, they go about 2-4 inches above your ankle.
It does not matter if they are odd; in fact, you can achive some nice results with ones that don't match.

Take the first sock (ie, the one that you want to be the body), and lay it out like so.

Make sure that it's inside out, and that the heel is flattened down.

Pin a straight line up the center of the sock; starting at the ankle (bottom), and finishing about an inch below the heel.
It may help if you draw a line with tailor's chalk or felt pen as a guide.

Thread your needle.
alternatively, use a sewing machine.

On the bottom of one of the halves, draw (or simply imagine) a paw-shape.

Start sewing from the outside, up the middle, leaving about 5mm from your pinning.

Stop sewing at the point shown. Tie a knot, and repeat on the other side.

Remove the needles, and cut right up the middle of your stitches.
Cut about 1cm further than your stitches go.

Turn your sock the right way round, through what will be your monkey-crotch. Ouch.
Put this aside for a few minutes.

Take the other sock, and press it out as shown.

Cut a long piece, from the toe all the way up to the hem at the top.
Cut out the heel, leaving a little seam allowance.

Pin the long piece, as shown.
Cut the toe away, and cut both of he other piece in half, too.
Pin as ilustrated.

Sew it all up.
I've added labels on the picture, so you can see what the things will be :)

Turn them all the right way out.

Using a little stuffing, pin the heel (now a nose) onto the front of your other sock.

You can use a slipstitch, a blanket stitch, or hey- why not a running stitch?

You can sew the monkey ear on in the same way.
Yay.

Sew Mr. Monkey's tail on.

Stuff the "arms".

Make little holes in your monkey where you want the arms to be.

Go up through the crotch, with the arm still poking through.

Sew around the hole, sttatching the two edges together.

Chose two buttons for eyes.

Take your monkey. Chose where the eyes will be.

Sew they eyes on. Add a mouth with backstitch. Lovely.

Grab some stuffing.

*ahem* stuff you monkey.

Make sure its even, with plenty in the legs, head and bum.

Blanket stitch his poor monkey-crotch closed.

Doneee :D

Why not experiment with clothing, etc for yur new best-friend?

Lovely ;)