Legionary: The Roman Soldier's (Unofficial) Manual
Roman Legionary 58 BC-AD 69 For such a small book, this one sure has a lot of good information!
Roman Military Dress
Roman Military Equipment from the Punic Wars to the Fall of Rome, second edition
The Roman Army: The Greatest War Machine of the Ancient World (General Military)
The Complete Roman Army (The Complete Series)
Roman Battle Tactics 109BC–AD313 (Elite)