Let's see...
After 5 moves in 10 years, I have weeded my book collection down to those I love too much to part with.
Janny Wurt's 'War of Light and Shadow' series (but I've had trouble getting through the last few books of hers.)
Guy Kay's Fionavar trilogy, beginning with "The Summer Tree".
Also by Kay: "A Song For Arbonne", and "Lions of Al-Rassan" I did not care much for "Tigana" and HATED "Under Heaven". It was just too bleak, and I never really got to care very much for any of the characters. "The Sarantine Mosaic" was pretty good, and so was "Ysabel", but I gave away my copy of "The Last Light of the Sun".
Most of Patricia McKillip's books, but especially her Riddlemaster of Hed trilogy.
Um, that's more than 10 books already....
Let's see...I loved Anne McCaffrey's Dragonriders of Pern series. The first few novels were the best, and the 3 book series about Menolly, the female harper were really good, but the books definitely went downhill near the end of her life. She actually altered the backstory of several of her characters noticeably towards the end, too, which REALLY bothered me. The standalone book about beloved Masterharper Robiton was the worst in this respect, and I gave it away not long after reading it.
For Sci-Fi, I have enjoyed some of Julie Czerneda's books, most especially "In the Company of Others", followed by her Trade Pact Trilogy "A Thousand Words for Stranger", etc. and the Web Shifter's Trilogy, "Beholder's Eye", etc.
Now, back to fantasy: Jennifer Roberson's "Tiger and Del" series. They're not deep, but they are a LOT of fun (Tiger rides a stud that is always trying to get the better of him, and is rather misogynist/chauvinistic, two things Roberson has a lot of fun with ).
I used to own nearly every novel in the Star Trek universe, but have pared it down to just two: "Vulcan's Glory" by D.C. Fontana, and "The Vulcan Academy Murders" by Jean Lorrah. Both are excellent reads.
Barbra Hambly: "Dragonsbane" and "Ladies of Mandrigyn" are her two best, though from different universes. I especially like the characters from these books. Dragonsbane features Jenny, a scorceress and her husband, Lord Aversin, dragonslayer and absent-minded intellectual, who is in charge of protecting The Winterlands. The ending of this novel, where Jenny has to make a very important choice between the things she loves will surely put a lump in your throat.
"Ladies" features Sun Wolf, a mercenary who is coerced into training a group of women to fight. He is deeply in love with Starhawk, a female mercenary. They are separated when the ladies kidnap him, and the pain of their separation, and eventual reunion in battle are highlights of a very well written novel.
To round out my favorite fantasy books, Tad Williams' Dragonbone Chair series. is marvellous. I didn't much care for his other books.
Now, to switch genres: I have read most of Louis L'Amour's westerns (my brother is a HUGE fan) but he doesn't hold a candle to Jack Schaefer, the author of Shane. If you can find a copy of "Monte Walsh" or "Mavericks" GRAB THEM!! He manages to put a sense of history into his novels that L'Amour does not, and he breathes a life into his characters that makes L'Amour's characters seem cardboard at best. His short stories are also very, very good, too, and will make you weep and laugh and wish for more. I was first introduced to him in High School, and though my tastes in reading have changed a lot since then, I still cherish his books.