I'm lucky enough to have his complete fiction in five volumes (recent Nightshade edition), most or all of the Ballantine Adult Fantasy PBs (the Lin Carter anthologies that the good Dr. recommends above), the complete poetry in three volumes (Hippocampus), and older collection of his non-fiction, his selected letters (Arkham House), the large beautiful bibliography, most or all of the Necronomicon Press single-story editions, the two Necronomicon trade paperbacks, and more that I'm forgetting.
I don't have much to brag about anymore, so thought I'd do so when I could... I do love CAS.