If one needs to add a column to a matrix as the first or the last column, here is more elegant method:
array = {{a, 1, 2}, {b, 2, 3}, {c, 3, 4}};
column = {x, y, z};
(* insert as the first column *)
Join[List /@ column, array, 2]
(* insert as the last column *)
Join[array, List /@ column, 2]
For other methods see the following MMa.SE thread and the threads referenced in it:
http://mathematica.stackexchange.com/q/44459/280
