Books 2 and 3 in the Jedi Apprentice series.

Book 2:

Qui-Gon Jinn's past is not at rest. How can he forge a bond with young Obi-Wan Kenobi while he is haunted by the betrayal of his first apprentice Xanatos? Xanatos was also a promising student, until the dark side of the Force intervened. Qui-Gon thought he was gone forever.
But now Xanatos is back. And he wants revenge.

Simple, brilliant story and great action. 4 dark former apprentices out of 4 boys not wanting to be farmers.

Book 3:

After Obi-Wan Kenobi and Qui-Gon Jinn are hijacked to the planet Phindar, they find themselves trapped in a world gone mad. The ruling Syndicat controls the people by erasing their memories. The planet's only hope lies with a band of thieving rebels.
Qui-Gon and Obi-Wan are caught in a mind war. And if they're not careful, their own pasts will be wiped out forever.

Interconnects with Book 2, just as that book interconnected with the first book. Great plot device in the Jedi being hijacked to a planet in dire need of their help. Fantastic subplot about the Padawan birthday gift (Qui-Gon gives Obi-Wan something a little...unexpected) and the villain weapon of the human memory wipe is great writing.

4 "Not so's" out of 4 "maybe I lie's"

As others have said these books give much needed depth to the Prequel setting and characters.

I've taken a break and randomly jumped into The Truce at Bakura.