If you enjoyed Williams's Augustus, do give Stoner and Butcher's Crossing a read. I "enjoyed" them even more than Augustus. Enjoyed is in quotes because they are both emotionally devastating -- Stoner more so than Butcher's Crossing. I didn't feel like myself for a week after reading Stoner and a decade later I still often think about it.
I read Stoner a month ago, and just finished Augustus. Both are among the best books I have read this year, so far at least. I’ll be picking up Butcher’s Crossing soon but needed some lighter reads in-between :)