First on my list is Forever Rose, by Hilary Mckay, the most recent book about the Casson family (Saffy's Angel, etc.). It came out in England last fall, but won't be out in the US till this summer. The copy I'm going to be reading is currently in New York, at my sister's house; every time I talk to her I encourage her to come visit, so as to bring it with her. I have also offered to pay for postage.
I am also looking forward to Lavinia, by Ursula Le Guin (April 2008), House of Many Ways, by Diana Wynne Jones (June 2008), and Knight Errant, by Patricia McKillip (Sept. 2008) (which shows up on the list of forthcoming books here at locus online). I also am looking forward very much to Megan Whalen Turner's next book, but she hasn't finished it yet. I think that all my life I will be looking forward to her next book, so I hope she outlives me.
I will eagerly pounce on Love (and Other Uses for Duct Tape) by Carrie Jones (sequel to Cybils finalist Tips on having a Gay (ex)Boy Friend).
Finally, and most obscurely, I'm looking forward with great anticipation to Kate at Melling, by Margaret Biggs. This is a new book written by the author of a great English girls school series (Melling being the school). The series, originally all published before 1960, has been republished by Girls Gone by Publishers, and the author has written this brand new story!
Colleen at Chasing Ray is kindly rounding up other lists of anticipation!