You know, I've read Le Guin, but the only thing I can think of by her right now is The Earthsea Trilogy
? If she's one of his faves, he'll already have these. I've only read one of John Ringo's but it was a "can't put it down" type of book (There Will Be Dragons
,) and I intend to locate copies of the sequel/prequel to this book.
If I remember correctly most of Le Guin's stuff is pretty much on the serious side so he would probably enjoy that one. Mercedes Lackey comes to mind although she's mostly Fantasy. Personally I always enjoyed Anne McCaffrey's books although some serious SF fans tend to look down on her as a hack writer (dunno why, all I ask out of a book is to be entertained and she does that very well.)
These days my absolute favorite author is Terry Pratchett as his books are funny, satirical, though-provoking and just generally a rollicking good read. His books are actually serious --- if you read between the lines
so to speak.
There's just too much to choose from. My sister brings me freebie copies from some of the conventions she attends and that's the way I find new authors these days. Although a lot of these do tend to be Baen Books since she's a friend of one of the editors and her husband.
I hope you're taking notes