I've got most of the Alias prequel books, plus one of the APO series - here's my list:
Prequels
Recruited
Disappeared
Sister Spy
Father Figure
Free Fall
Infiltration
Vanishing Act
Skin Deep
Shadowed
APO Series
Two of a Kind?
I still don't have A Secret Life from the prequels yet, but I'd like to get it - and I'm not planning to get the Vaughn prequel books.