Advice on buying a wide-angle?

[masp]

After looking at some of the amazing wide-angle landscape photos in the latest National Geographic (read it! ), I've decided I really need a super wide-angle. Does anyone have any suggestions on what would be a good buy for $600 or less? And is a 10mm wide angle the widest available right now?

I've been eyeing the Tokina 12-24 f/4 or 11-16 f/2.8 lately, though I wonder how Tamron's 10-24 or Sigma 10-20 offerings compare. The Sigma is the slowest of the bunch, while the Tokina is the fastest and not really all that much more expensive or heavy and probably has a better build knowing Tokina. Also I might go with a old manual focus version if I knew which ones to seek or avoid.

Edit: Sony's wide-angle seems to be a poor performer and rather expensive to boot.

It seems that the increased depth of field from wide angles makes autofocus less necessary for most subjects (maybe just pre-focus using hyper focal distance?) and besides, landscapes usually won't run away from you.