Bernat Sox is an acrylic/nylon mix which can be knit on 2.25mm needles making it pretty useful. The yarn information says a 3.25mm needle but having used this yarn I'd say that was far too big. Apparently it's been discontinued by Bernat, but it's still coming up on Ebay and you may find it on sale somewhere while they clear out stocks.
It's available in plain colours and variegated (links are to the Yarndex pages of the yarn). You can see the Sox Multi projects on Ravelry here and the Sox Plain projects here.
Examples of Sox socks:
There are 203 yards per ball meaning that you will need 2 for an adult pair of socks.
Some people like acrylic yarn, personally this yarn makes my teeth itch and I only used it as the variety of vegan sock yarn a few years ago was terrible. I do like the socks I've made with it and they appear to be lasting forever, but I won't be buying any more.
Anna in Liverpool England