I haven't read any of his books any suggestions as to a good one to start with?
They are a series so its best if you start at the beginning .
This list is NOT the order they were written , the first 2 are actually the last ones written, but they introduce the character and tell of his recruitment , training, and first missions .
http://en.wikipedia.org/wiki/Vince_Flynn#Chronological_Order_Of_The_Mitch_Rapp_StorylineChronological Order Of The Mitch Rapp Storyline
The Mitch Rapp story begins with American Assassin [2010], followed by Kill Shot [1999], Transfer of Power [1999], The Third Option [2000], Separation of Power [2001], Executive Power [2002], Memorial Day, Consent to Kill, Act of Treason, Protect and Defend, Extreme Measures, Pursuit of Honor and The Last Man (November 2012).
American Assassin (Mitch Rapp #1)
(2010) - ISBN 978-1416595182
Kill Shot (Mitch Rapp #2)
(February 7, 2012) - ISBN 978-1416595205
Transfer of Power (Mitch Rapp #3)
(1999) - ISBN 0-671-02319-5
The Third Option (Mitch Rapp #4)
(2000) - ISBN 0-671-04731-0
Separation of Power (Mitch Rapp #5)
(2001) – ISBN 0671047337
Executive Power (Mitch Rapp #6)
(2002) - ISBN 0-7434-5395-6
Memorial Day (Mitch Rapp #7)
(2004) - ISBN 0-7434-5397-2
Consent to Kill (Mitch Rapp #8)
(2005) - ISBN 0-7432-7036-3
Act of Treason (Mitch Rapp #9)
(2006) - ISBN 0-7432-7037-1
Protect and Defend (Mitch Rapp #10)
(2007) - ISBN 978-0743270410
Extreme Measures (Mitch Rapp #11)
(2008) - ISBN 978-1416599395
Pursuit of Honor (Mitch Rapp #12)
(2009) - ISBN 978-1-4165-9516-8
The Last Man (Mitch Rapp #13)
(November 13, 2012) - ISBN 978-1416595212
The Survivor (Mitch Rapp #14)
(Fall 2013)
Term Limits (not part of Mitch Rapp series)
(1997) - ISBN 0-671-02317-9 : In the Rapp-Universe But Not A Mitch Rapp Story