Jedi Apprentice is fantastic. Shatterpoint is a nice departure from the general prequel crap.
The Han Solo Adventures are still the best to me. Closest to the escapist spirit of the films.
The Thrawn trilogy is a close second. Still great after all these years. I, Jedi is pretty good from what I remember. You can't go wrong with most of the Bantams. From the NJO on I just gave up. I've read numerous books since then and have officially just given up.
Other notables I can think of: Han Solo trilogy, Shadows of the Empire, X-Wing series, Courtship of Princess Leia, Jedi Academy Trilogy, Hand of Thrawn Duology, and some of the "Tales from" collections.