This picker seems nice. I'm bookmarking it for any case where a complex datepicker is necessary.
For people looking for keyboard / accessibility support, I personally don't think a datepicker should be attempting to handle those concerns; it's more of a UI polish layer than a primary input method.
On that note, if you're looking for something significantly more lightweight (~8k minified) and easily skinnable, you could check out my own jQuery.minical: