Extreme Double Knitting. You can pre-order it now from Cooperative Press for a discount, and you should- even if you don't think you're crazy enough to ever attempt his patterns, it is a book worth owning for the sheer mind blowing inspiration of his work.
I'd be willing to bet that in 10 years, Alasdair will be to double knitting what Kaffe Fassett is to colorwork, or Alice Starmore to cables. Maybe 5 years. Maybe one. Don't believe me? Check out the photos on his blog. Or, scroll through my old entries- remember this photo from Fiber Camp back in March? That's Alasdair, holding several of the designs that will be in the book. You can also get a few of his patterns individually on ravelry.
Alasdair- keep being awesome! Your work inspires me.