Is a Tortillah considered lechem (bread), pas habab'knisin (cake/cracker/pie which assumes the status of bread AIUI when one "makes it a seudah"), or is it a stam mezunos? I haven't seen it explicitly mentioned on the various b'rachos lists.
Are you asking about wheat or corn flour tortillahs?
Wheat flour tortillas are essentially a flat bread, a bit thinner than pitas. ( http://en.wikipedia.org/wiki/Flour_tortilla ) . I see no reason that their bracha should be anything other than HaMotzi as they do not fit into any of the definitions of Pas HaBa'ah B'Kisanin.
Corn flour tortillas are made with corn meal ( http://en.wikipedia.org/wiki/Corn_tortilla ) and like anything made with corn meal (such as corn chips or tortilla chips) their bracha is Shehakol.
I do not have written sources for you on these exact items, but based on basic Hilchos Berachos" these are the correct berachos for these two items.