Most people know this one, but a friend asked me to put a vid up.
How:
-Get a reasonable distance from the rock in a banshee(as shown in the vid).
-Drop down, then fly up level with the rock wall like I do.
-Don't touch the wall, it messes the glitch up.
-Half way up the flat side of the rock (the spot that i go to), press 'e' to get out.
-When see yourself getting out of the banshee, lean forward.
-As soon as you are out of the banshee walk forward by pressing 'w'.
with any luck youre now on the rock! Dont be put off if you dont get it first time.
hope this helps, but if you have any questions (im a crap teacher) then leave a comment, and i'll get back to you :)
visit... http://www.bebo.com/atillathehunch = me :D