AMXX 1.70 (previous versions may work)
walljump_str "300.0" - How much strength it pushes you upwards.
walljump_num "3" - How many wall jumps you can do without touching ground.
walljump_team "0" - Choose which team can use the walljump. 0 = both
twistedeuphoria - Got some stuff from his multijump.
To wall jump, simply jump towards a wall holding your jump button, when you hit the wall, you'll bounce off it. If you push towards the wall with your movement keys while attempting a walljump, you won't bounce, but jump a bit higher.
Note: The plugin is really basic atm, and the angle you bounce off of the walls is the same angle as when you jumped, but reversed. I'll release a newer version later to enhance the angle you wall jump at.