There are two great looking short story anthologies due out this month, both containing previously unpublished short stories by Gene Wolfe.
Stories: All-New Tales. Edited by Neil Gaiman and Al Sarrantonio. Headline, 2010.
Early reviews of this collection have been overwhelmingly positive, with the LA Times claiming it is "breaking fantasy from the genre ghetto." According to Crime and Publishing, "This anthology grew out of Neil Gaiman and Al Sarrantonio’s frustration with the boundaries that genre has placed on writers." That sounds fantastic to me! The stories I love most are always those which challenge genre boundaries and create imaginative blends of established genre conventions. The anthology's warm reception isn't a huge surprise, given it has such an amazing line-up of authors, including Neil Gaiman, Diana Wynne Jones, Michael Moorcock, Tim Powers, and many other big names. Wolfe's contribution is called "Leif in the Wind." The full table of contents is online at SF Signal. Stories is due out on 15 June (BookDepository).
Swords & Dark Magic: The New Sword and Sorcery. Edited by Jonathan Strahan and Lou Anders. Eos, 2010.
I haven't seen any reviews of this anthology yet, but again the authors all seem to be quite big names from the fantasy genre. Wolfe's story is titled "Bloodsport." I am also very excited to see Bill Willingham has contributed a story called "Thieves of Daring"—I absolutely adore Willingham's Fables comic book series. Check out the full table of contents is online at SF Signal. The Swords & Dark Magic trade paperback is due out on 1 July (BookDepository). A Limited Edition hardcover will also be available from Subterranean Press.
UPDATE (15/6/2010): Seems I missed another one coming out soon...
Gateways: Original New Stories Inspired by Frederik Pohl. Edited by Elizabeth A. Hull. Tor, 2010.
This anthology is a tribute to Pohl, and includes many great authors, including Neil Gaiman, Greg Bear, and Cory Doctorow. Wolfe's story is titled "King Rat", and I don't believe it has been published elsewhere. The full contents is available on Pohl's fantastic blog. The hardcover book is due out on 6 July (BookDepository).