China Mieville is probably the most popular after Gaiman. His most popular works include Perdido Street Station, The Scar, and The Iron Council. PSS was his first, probably the best place to start.
Jeffrey Ford is another brilliant mind. He has a series called "The Well-Built City" which starts with [ame=http://www.amazon.com/Physiognomy-Jeffrey-Ford/dp/0380793326/ref=pd_sim_b_shvl_title_2/103-0220401-0351813?ie=UTF8&qid=1190920242&sr=8-5]The Physiognomy[/ame].
However, my favorite is Jeff Vandermeer. His most essential work is [ame=http://www.amazon.com/City-Saints-Madmen-Jeff-Vandermeer/dp/0553383574/ref=pd_bbs_sr_1/103-0220401-0351813?ie=UTF8&s=books&qid=1190920381&sr=1-1]City of Saints and Madmen: The Book Of Ambergris[/ame]. This is actually a collection of short stories set in his mythical and overall fucked city of Ambergris. CoSaM, while an amazing read in and of itself, provides essential background information necessary to fully appreciate Vandermeer's first true novel, [ame=http://www.amazon.com/Shriek-Afterword-Jeff-VanderMeer/dp/0765314665/ref=pd_bbs_sr_2/103-0220401-0351813?ie=UTF8&s=books&qid=1190920493&sr=1-2]Shriek: An Afterword[/ame]. Basically Shriek is the sequel to one of the short stories in CoSaM, written from the perspective of the sister of the narrator of the short story, which is a history of Ambergris. So I wholeheartedly reading CoSaM, and if you think its cool, then check out Shriek. Taken together, they are one of the most outstanding stories I've read.
For a quick read of Vandermeer's not set in Ambergris, check out his novella Veniss Underground, which is horror/sci-fi. Its layers and layers and layers of fucked-upness. Layers, I tell you.
So while I'm digging up those amazon links, I stumble across this upcoming anthology: [ame=http://www.amazon.com/New-Weird-Ann-VanderMeer/dp/1892391554/ref=pd_bbs_3/103-0220401-0351813?ie=UTF8&s=books&qid=1190920669&sr=1-3]The New Weird[/ame], ed. Ann and Jeff Vandermeer. The blurb sums up the new weird well:
"This avant-garde anthology that presents and defines the New Weird?a hip, stylistic fiction that evokes the gritty exuberance of pulp novels and dime-store comic books?creates a new literature that is entirely unprecedented and utterly compelling. Assembling an array of talent, this collection includes contributions from visionaries Michael Moorcock and China Mi?ville, modern icon Clive Barker, and audacious new talents Hal Duncan, Jeffrey Ford, and Sarah Monette. An essential snapshot of a vibrant movement in popular fiction, this anthology also features critical writings from authors, theorists, and international editors as well as witty selections from online debates."
Also, here is Jeff Vandermeer's working definition for New Weird, taken from a recent entry on his blog:
"New Weird is a type of urban, secondary-world fiction that subverts the romanticized ideas about place found in traditional fantasy, largely by choosing realistic, complex real-world models as the jumping off point for creation of settings that may combine elements of both science fiction and fantasy. New Weird has a visceral, in-the-moment quality that often uses elements of surreal or transgressive horror for its tone, style, and effects? in combination with the stimulus of influence from New Wave writers or their proxies (including also such forebears as Mervyn Peake and the French/ English Decadents). New Weird fictions are acutely aware of the modern world, even if in disguise, but not always overtly political. As part of this awareness of the modern world, New Weird relies for its visionary power on a ?surrender to the weird? that isn?t, for example, hermetically sealed in a haunted house on the moors or in a cave in Antarctica. The ?surrender? (or ?belief?) of the writer can take many forms, some of them even involving the use of postmodern techniques that do not undermine the surface reality of the text."