Simon R. Green - Author of the Nightside series, Deathstalker series, and numerous other fantasy/sci-fi/modern fantasy blending books. All of his books are easy to pick up, quick to read, and feature resourceful heroes who rise to every challenge. Sometimes it may seem a little too easy, but sometimes I need "popcorn fiction."
Robert Jordan - Robert Jordan's Wheel of Time series (finished in part by the next author on the list) is pretty much the opposite of popcorn fiction. It's heavy in a way only George RR Martin really rivals. There are allusions to basically every major religion in the world and a few that aren't so major. Each name has meaning and there's a broad tapestry of characters who come and go. The books are definitely slowed by that, but the complexity of vision is something I could only aspire to in my wildest dreams.
Brandon Sanderson - One of the coolest things about Brandon Sanderson (and the next author on the list after him) is his high interaction with fans. His insights while re-reading and finishing the Wheel of Time series after Jordan's death brought even more depth to my understanding of the books. He's described (I'm paraphrasing here) his new novel The Rithmatist as being like "StarCraft done with magic," which is a pretty nifty hook to catch my interest. He talks to a lot of folks on twitter and shares a lot of insights.
Jim Butcher - Also a big fan interaction author, Jim Butcher writes the Dresden Files series. These books begin to touch on the complexity of Jordan's allusions and plot complexity while still having more of an accessibility of Simon R Green's works. Butcher tweets about his life in roleplaying and has let his books become a setting in the Fate system. He's also answered some direct questions about the Dresden Files over twitter. His bio photo is basically the greatest thing ever.
Cherie Priest - Queen of Steampunk. Her Clockwork Century series is basically the pinnacle of meshing steampunk sci-fi sensibilities with alternate history fiction's "accuracy spun in a different direction," which is most definitely a term I'm making up. Each book pushes you to find the revelation of it's steam-powered namesake while blindsiding you with other fantastic things like zombies. She's also on twitter and out at cons quite a bit.
Seanan McGuire/Mira Grant - Yet another author on twitter. A fairly prolific writer, blogger, tweeter, con-er, and podcaster, my favorite of her works are under the penname Mira Grant, where she authored the Newsflesh trilogy (and quite a bit of short fiction in the same setting). I like that enough that I've already written about it here.
Neil Gaiman - Kind of the godfather of the modern blogging/tweeting author. Gaiman has done everything from TV (Babylon 5), comics (Sandman), movies (Mirror Mask), to novels (Good Omens, Stardust, and so on). Another font of advice and knowledge on writing and unafraid to get into a conversation with fans. His relationship with Amanda Palmer is probably the prototype for a successful geek relationship, too.
Chuck Wendig - I've probably learned more about writing from Chuck Wendig than from any other single person, despite never having met him. His books on writing are excellent, dripping with sarcasm and wit while still pounding home important information that can help an aspiring writer focus. His novel Dinocalypse Now is a great blending of roleplaying (it's set in the Spirit of the Century world) and fun writing.
John Scalzi - Another great satirist. Scalzi is a sci-fi titan that seems to mix equal parts Douglas Adams and Robert Heinlein. His Old Man's War series is a great look at a potential fix Earth might use someday when in need of soldiers and Red Shirts is basically the best Star Trek parody ever written. Seriously, it's a must-read.
Christie Golden - Christie Golden has written a little bit of everything, from Star Trek to Ravenloft. Most of what I've read from her is in the WarCraft and StarCraft universes. Her take on Jim Raynor and Sarah Kerrigan in Devil's Due and Flashpoint really added tons of depth to the first two chapters of StarCraft II, and I'm sure that the material from the Dark Templar Saga and Project Blackstone have big implications for the third chapter.
Nate Kenyon - I think it's awesome that Nate Kenyon took some time to speak with me at Blizzcon mentioned to me about his experience writing StarCraft: Ghost: Spectres. I never spoke with him about my own writing, but hearing his process meant a lot to me. It's extremely impressive to me how he can switch from sci-fi mystery writing to horror fantasy writing seemingly without much difficulty and his versatility is amazing.