Here's a quick and dirty pattern to make your very own. You'll need one pair of socks to make one monkey. One sock will be the body and the other sock will make the mouth, ears, arms and tail. If you're making it for older children you can use buttons for eyes. Since I tend to make mine for babes I just use a needle and black thread and stitch eyes and nose holes on to avoid the choking risk.
Tips: If you have a sewing machine - use it!! I did this project by hand the first time, and it did not stand up to the rigors of a 2 year old! 2) I've done this with christmas print socks, solid socks and red heel socks. Red heel always come out the best in my opinion, but any sock will do!