The following is a simple example for how I was thinking of approaching the problem.
(* Mathematica 7 *)
Plot3D[ Sin[x] Cos[x], {x, -Pi, Pi}, {y, -Pi, Pi},
AxesLabel -> {
Rotate[ Grid[{ {"PEAK", " ","TROUGH"}(*Format as needed*)},
Alignment -> Left
], -0.13Pi(*Rotate to align to x-axis for aesthetics*)], "Y", "Z"},
Ticks -> {None(* Remove x-axis ticks *), Automatic(*Keep Y ticks*), Automatic(*Keep Z ticks*)}]
