Yes, I have many recomendations:
First of all, you can't go wrong with Stephen Dando Collins' books. He has three so far:
Nero's Killing Machine - The True Story of Rome's Remarkable Fourteenth Legion
Cleopatra's Kidnappers - How Caesar's Sixth Legion Gave Egypt to Rome and Rome to Caesar
Caesar's Legion - The Epic Saga of Julius Caesar's Elite Tenth Legion and the Armies of Rome
These are all unit histories from a guy who's spent his life researching Roman Legions. I'd say you can trust him. He also lists sources and the books read like novels, really. All quotes are taken from ancient texts. If they don't hook you, nothing will. Personally I love his style.
Then of course, you can go to the ancient texts yourself. Caesar's Gallic Wars is a first-hand account (with some first hand embellishments) and Tacitus' "Annals of Imperial Rome" is pretty darn good too. You also have Seutonious' "The Twelve Caesars" and Plutarch's "Lives". There are many others out there, these are the only one's I've dipped my nose in.
Not completely Roman - but "Fighting Techniques of the Ancient World" by Simon Anglim, Phyllis G. Jestice, Rob S. Rice, Scott M. Rusch, and John Serratt is very intersting.
Getting back to Rome and specifically her Legions, anything Adrian Goldsworthy won't let you down. "The Men Who Made Rome" is good, and he also has books that are specifically geared towards the Roman Army. "Roman Warfare" (Edited by John Keegan) is a pocket sized book thatgoes all the way from the Kings to the Decline. A good read, but not a long one.
"The Making of the Roman Army - From Republic to Empire" by Lawrence Keppie is informative, but I find his stlye a bit dry.
"Chronicle of the Roman Republic" by Philip Matyzak has good information but its primary concentration is not the Legions. Same with "The Romans - From Village to Empire" by Boatwright, Gargola and Talbert. This was actually the text for my History of Ancient Rome class. It's very dry but the most informative book I've ran across on the topic yet. Again, military is not the primary focus, but it is certainly included.
Finally, if you're just looking for a bathroom reader on the army, check out "The Roman Army - Legions, Wars and Campaigns" by Nigel Rodgers. It doesn't go into too much depth but is a good starter and has a lot of cool illustrations.
Anyway, I'd say that should get you started
Edit - when going for the ancient texts, I'd recommend any translation other than Penguin's Classics. I really, really, really hate Legions being called "brigades", but maybe that's just me.
