I'm only listing nominees in fiction. A couple of notes on other categories. The only prominent SF movie I've seen is Avatar, which I thought both beautiful and stupid. In the Fan Writer category I will again nominate both James Nicoll and Abigail Nussbaum, and urge others to check their work out as well. I am also going to nominate Niall Harrison, for his consistently stimulating work at the Vector blog, Torque Control, and for his reviews (mainly at Strange Horizons), and Graham Sleight, primarily for his series of articles reexamining classic SF writers, in Locus.
I'm only nominating three, as I feel I haven't read enough. But I wanted to get my oar in for the two McAuley novels, which may be at a disadvantaged, as having ambiguous publication dates (for Hugo recognition): each was published a year later in the US than in the UK. And I loved Scott Westefeld's Leviathan, though it's not really a complete story. So ...
The Quiet War, by Paul McAuley (Gollancz (2008, UK), Pyr (2009, US))
Gardens of the Sun, by Paul McAuley (Gollancz (2009, UK), Pyr (2010, US))
Leviathan, by Scott Westerfeld (Simon Pulse (2009))
I thought this a slightly down category this year. But I haven't seen two very well-regarded ones: John Scalzi's Nebula nominee The God Engines, and Vandana Singh's "Infinities". My nominees:
"Crimes and Glory", by Paul McAuley (Subterranean, Spring)
The Push, by Dave Hutchinson (NewCon Press)
Horn, by Peter M. Ball (Twelfth Planet Press)
"Broken Windchimes", by Kristine Kathryn Rusch (Asimov's, September)
"Vishnu at the Cat Circus", by Ian McDonald (Cyberabad Days)
The last two made the list out of a small pack which also included "Earth II" by Stephen Baxter (Asimov's, July), and "Halloween Town", by Lucius Shepard (F&SF, October-November).
This is always the toughest category for me. My top five ended up being:
"Things Undone", by John Barnes (Baen's Universe, December)
"Eros, Philia, Agape", by Rachel Swirsky (Tor.com)
"The Island", by Peter Watts (The New Space Opera 2)
"This Wind Blowing, and This Tide", by Damien Broderick (Asimov's, April-May)
"The Qualia Engine", by Damien Broderick (Asimov's, August)
But there is a horde of stories very close (and my final ballot may end up changing). These are: Robert Charles Wilson's "This Peaceable Land; or, The Unbearable Vision of Harriett Beecher Stowe" (Other Earths); John Kessel's "Events Preceding the Helvetican Renaissance" (The New Space Opera 2); Sarah Monette and Elizabeth Bear's "Mongoose" (Lovecraft Unbound), John Langan's "Technicolor" (Poe), and Chris Adrian's "A Tiny Feast" (The New Yorker, April 20).
My short story nominees will be:
"Three Twilight Tales", by Jo Walton (Firebirds Soaring)
"The Radiant Car Thy Sparrows Drew", by Catherynne M. Valente (Clarkesworld, August)
"Child-Empress of Mars", by Theodora Goss (Interfictions 2)
"On the Human Plan", by Jay Lake (Lone Star Stories, February)
"A Story, With Beans", by Steven Gould (Analog, May)
A couple more Clarkesworld stories vied for a spot on the ballot (Kij Johnson's "Spar" (October), and Lavie Tidhar's "The Dying World" (April)).
My five nominees are Toiya Kristen Finley, Rochita Loenen-Ruiz, Eric Gregory, Saladin Ahmed, and Alice Sola Kim, which strikes me as a very diverse group, without me even trying. I've reprinted a story by Kim, and will be reprinting one by Finley, and hope to announce soon another reprint from among this group.