Originally this category was "Best Professional Magazine," but that was changed back when books and original anthologies began to shove the prozines aside and assume more importance in the field, the idea being that now book editors would be able to compete for the Hugo as well. That sounded good in theory, but didn't work in practice, since book editors were seldom credited and the readers didn't know who they were. So the magazine editors continued to dominate.
Last year, however, the award was split in two. Now we have a Hugo for "short form" editing and one for "long form" editing.
The short form nominees are going to be the usual bunch of suspects, the magazine and anthology editors who have filled the ballot for years. The best of them, to my mind, is still GARDNER DOZOIS, and I expect I will be nominating him again. He brought ASIMOV's to its present position as the best magazine in the field, still edits his BEST OF THE YEAR, and has also edited various original anthologies, some published, some in the pipeline.
The long form editors -- the book editors -- are still largely unknown to the general reader. Let me mention a couple of them who deserve a nod. 2007 was the last year of ELLEN ASHER's long tenure at the Science Fiction Book Club, where she had been the editor for as long as I've been publishing. It was a distinguished career, and Ellen had the daunting task of reading almost all the SF and fantasy being published and selecting the best of it for her club members. She's never been honored with a Hugo, and I think it's past time. She'll be on my nominating ballot, and I urge you all to remember her on yours.
I will also be nominating my own editor, ANNE LESLEY GROELL of Bantam Spectra. She's been my editor since the first volume of A SONG OF ICE AND FIRE, and she's been terrific every step of the way. If I survive this series, it will be in no small part thanks to Anne, so go and nominate her too!