I've been knitting a lot of socks in the past few months. Ann Budd's article in Interweave Knits on toe-up socks got me re-interested in sock knitting, and that interest quickly became an obsession (witness my entire birthday present list).
There are many sock yarns out there, and I've only tried a few so far; some have produced successful, happy socks, and others have disappointed.
So far, the winner is KnitPicks Essential and Essential Tweed. Besides coming in a good range of colors, knitting up beautifully with no splitting, and being the best bang for your buck, it goes through the washer the best.
Shelridge Farm's fingering weight, while not specifically a sock yarn (ie, it is pure wool with no nylon or other material mixed in), it makes beautiful socks that go through the wash on cold. The finished product is a bit heavier than Essential/Essential Tweed, so these are socks that I save for colder days. Their color choices are almost unlimited so I know I'll be visiting them at Stitches this year.
Jojoland Melody is a good runner-up to Shelridge. Again, not specifically a sock yarn. The drawbacks to Melody is that there is a bit of piling where my boots rub against the sock and that there is a little bit of shrinkage when put through the washer. I've made a couple of stoles using Melody which is honestly a better use of this yarn.
I also used a merino/cashmere blend from Jojoland for my first pair of socks, and they turned out so well: this yarn was a dream to work with and the resulting sock was a pleasure to have on my foot. And then I made the stupid, stupid mistake of putting them in the wash. They felted to the point of not being wearable at all. Duh.
XXL Trekking is ok to work with. I found it a little slippery (for lack of better tactile description); the sock that it produced again was ok but didn't delight my feet the way Essential does.
I'm knitting for StellaPop knits again, so my sock-knitting time has been reduced. I won't be churning out a pair of socks every ten days or so, unfortunately. Next month, my sock-of-the-month birthday gift starts, exposing me to more new sock yarns. It will be interesting to see what comes.