500 Days of Summer, Avatar, The Hangover, The Hurt Locker and A Serious Man has been honored with WGA nominations for original screenplay whereas Crazy Heart, Julie & Julia, Precious, Star Trek and Up in the Air took the honors in the adapted category. 

James Cameron gets the credit for the Avatar script, Mark Boal for The Hurt Locker, Scott Neustadter and Michael H. Weber for 500 Days of Summer, Jon Lucas and Scott Moore for The Hangover and Joel Coen & Ethan Coen for A Serious Man. 

Scott Cooper’s script for Crazy Heart landed a nomination for adapted screenplay honor along with Nora Ephron for Julie & Julia, Geoffrey Fletcher for Precious, Roberto Orci and Alex Kurtzman for Star Trek and Jason Reitman and Sheldon Turner for Up in the Air. 

The Writers Guild of America will announce and celebrate the winners February 20, 2010 in Los Angeles and New York.

Some films didn’t make the nomination because of ineligibility such as Inglourious Basterds, District 9, An Education, Fantastic Mr. Fox, In the Loop, The Road, A Single Man and Up. Understanding method to determine eligibility is beyond my comprehension, but you can visit WGA website to get the low-down and the complete list of nominees.  

(Source)