There are five TCW spinoff novels: The Clone Wars and Wild Space by Karen Traviss, and Wild Space, Clone Wars Gambit: Stealth, and Clone Wars Gambit: Siege by Karen Miller. I haven't read any of them so I don't know if they're any good or not but they do feature TCW characters like Ahsoka, Rex, Lok Durd, and Wullf Yularen. For pre-TCW Clone Wars material, Shatterpoint, Dark Rendezvous, and Labyrinth of Evil are the essentials, along with Dark Horse's line of Clone Wars comics, which were recently republished in three Omnibuses. I don't know if you have any interest in comics but these are quite good and feature Asajj Ventress as a recurring character, before her backstory and character arc were rewritten by TCW. The only books in this time period worth reading are Knight Errant and Lost Tribe of the Sith, both by John Jackson Miller. The others are the mediocre Darth Bane Trilogy and a series of subpar tie-ins to the MMO The Old Republic. Mostly, the pre-PT era is dominated by comics: Dawn of the Jedi is a current ongoing series set over 25,000 years before the movies. It's about how the Jedi Order was first formed, before the Galactic Republic even existed. I haven't read any of it but the creative team behind is very good. Only the first story arc has been collected in trade paperback so far, though, so you'd have to read back issues to catch up. There's also a novel set in this time period that's coming out soon, called Into the Void. Tales of the Jedi is a comic series from the mid-1990s about some of the first wars between the Jedi and the Sith. Unfortunately, it's not very good (except for the final story arc, Redemption, which is excellent). If you're interested in this era, though, I guess it's fairly essential. The whole series was collected in two Omnibuses a few years ago. Knights of the Old Republic is kind of a prequel series to the KOTOR video games, although it revolves around an entirely different cast with infrequent cameos from the game characters. It follows the adventures of a Jedi Padawan framed for murder as he and his friends try to evade both the Jedi Masters who framed him and the war between the Mandalorians and the Republic. The whole series is available in ten TPBs, and later this year Dark Horse is going to start republishing it in a series of Omnibuses. Knight Errant is a series from the same writer as KOTOR, set a few thousand years later during the New Sith Wars. The Knight Errant novel I recommended earlier takes place at the same time as this series and involves the same characters. I haven't read this comic but I've heard good things. It's pretty short and was collected in three TPBs. Jedi vs. Sith is the story of the end of the New Sith Wars, the conflict that resulted in the apparent destruction of the Sith, as mentioned in the prequels. It's quite dark and brutal, as it shows how desperate the Jedi have become to end this war that has stretched on for a thousand years, and how much reduced they and the Sith both are from their typical glory and power. This story was somewhat retold in the first book of the Darth Bane Trilogy, but it was retold very poorly with none of the nuance, pathos, or attention to character and detail. It's my personal favorite comic from this era, but if you have no interest in comics I guess that's irrelevant.