I first discovered his writing when I read his Jedi Academy trilogy (Jedi Search, Dark Apprentice, Champions of the Force). While Timothy Zahn received all the praise for his Star Wars novels, I personally enjoyed Anderson's better. KJA has a knack for capturing the feel of the existing franchise he's adapting and its characters. His three novels were fun and I could completely visualize them as big screen sequels to George Lucas' saga. He returned to the Star Wars universe with another novel, Darksaber.
His X-Files books (Ground Zero, Ruins, Antibodies) were equally excellent -- I remember reading them and thinking they measured up to the finest adventures of Scully and Mulder as they investigated the paranormal.
He also wrote the novelizations for The League of Extraordinary Gentlemen and Sky Captain and the World of Tomorrow, as well as spin-off's of Titan A.E. (Akima's Story and Cale's Story).
Anderson is also a terrific collaborator. He and his wife wrote another popular Star Wars series, this one for young adult readers, Young Jedi Knights (which I believe consists of 14 books). He has also teamed up with Doug Beason for a number of acclaimed science fiction tomes: Lifeline, The Trinity Paradox, Assemblers of Infinity, Ill Wind, Virtual Destruction, Fallout, Ignition, and Lethal Exposure. His most recent popular collaboration has been the continuation of the Dune saga with Brian Herbert -- eleven books so far, and counting.
His original stories are proof that he is more than a write-for-hire hack. His Terra Incognita fantasy series includes The Edge of the World, The Map of All Things, and The Key to Creation. His hard science fiction epic, Saga of the Seven Suns, is arguably his greatest accomplishment -- Hidden Empire, A Forest of Stars, Horizon Storms, Scattered Suns, Of Fire and Night, Metal Swarm, and The Ashes of Worlds (not to mention the graphic novel prequel Veiled Alliance.)
He's also written the Superman book The Last Days of Krypton and the Superman/Batman team-up Enemies and Allies. His short stories have been collected in Dogged Persistence and Landscapes. He worked with Dean Koontz on Frankenstein: Prodigal Son and with Harlan Ellison on The Outer Limits: Armageddon Dreams. He edited a great series of Star Wars shortstories: Tales from Mos Eisley Cantina, Tales of the Bounty Hunters, and Tales from Jabba's Palace. He has started a new sci-fi series with Brian Herbert called Hellhole.
There's plenty more, but you get the gist. If you're looking for some last-minute summer reading, you won't go wrong with the books of Kevin J. Anderson.