Hi all, this will be updated as I find more and more cool hidey spots and exploits for BG's.
Here is this weeks first hidey spot, now I've looked around the site and If these already exist on the site I apologise.
Warsong Gulch
Horde hidey spot #1 (1.12)

CONGRADULATIONS!!! You’re there. Sit down, drink up, and own alliance.
Horde hidey spot #2 (1.12)

Code:
This spot is achieved the same way as spot #1 but you run along the
top and around the top of the east wall its kinda tricky so if you still cant
get it ill post a guide.
Alliance hidey spot #1 (1.12)
Code:
Ok the Alliance one enables you to get into there garden on the third floor.
I'm not going to post information on this as it is plastered all over the web.
The best source for this is mmowned's search, give it a go.
I did not find the “Alliance Garden” exploit so kudos to the finder.
Whoever that may be :)
Alliance hidey spot #2 (1.12)

Code:
This one is pretty sweet since its very easy and no one seems to know about
it, to access this spot go behind the alliance GY and jump up against the wall.
When you cant go any further up because of the roof, do a wall jump out
and then back in to get on top.
If you're still having trouble and cant get it ill post a guide.
Eastern Plaguelands
Top of a Tower (1.12) Without Hacks

Guides
Wall Jumping Breakdown (1.12)
Code:
My character here is standing outside of Orgrimmar, so for you on the horde
side who wish to follow this guide to the exact location I’m just outside to
the west in Rocktusk farm.
First of all we need to find a nice position to start, as you see with my
Undead Priest here I have walked as far up the wall as I possibly can.
Now that I have found my starting location I need to position my Priest
properly.
My goal here is to position her so she won’t slide off, I want her to land
completely horizontal with the wall.
This varies on different surfaces. Some walls allow you to make very steep
inclines as others may not let you jump at all.
Once positioned I will make my first jump by tapping forward and jump at the
same time. This may take a bit of getting used to, if you still find it hard
tap forward then jump straight after.
See how the Priest landed, almost as if there is an invisible ledge there.
She is completely horizontal with her left foot stuck into the wall.
If you have done it correctly you should be in a similar position.
Now for the tricky part, I need to reposition my character for the next jump.
This time I don’t want to face her in the direction I will be jumping but ever
so slightly out from the wall. Usually if it’s not much of a curved wall your
character should be readily positioned for the next jump.
There are a few reasons why I want my Priest facing out or along the wall
and not to where I’m jumping, one is simply the fact that jumping up an
un-walkable wall will cause you to slip down, however jumping along the wall…
Ok now my Priest is positioned on the wall I need to face the camera in the
direction I want to jump. In the screenshot I’ve chosen to make an incline on
the jump. dont let go of the right mouse button as your character will then
turn and face that direction, keep it pressed until after the jump.
Following the same principle of the previous step, I tap forward and jump.
Phew, I made it. Now that I’m up, the new found area is walkable so I can
walk around freely. And find the next hill I want to wall jump along.
I chose this area because of its simplicity. Even though only two jumps were
used in this guide it is possible to use endless amounts if used correctly.
Hope this was helpful. I’d love to hear of any wall jumping places you have
found.
Ok this is it for now; I will update it with some more exploits as soon as I gather some screenshots.
As for now use the above information wisely. With the horde hidey alone I have found many, many secret spots..
Including behind the Horde flag. It's not an easy spot to get to but I'm positive you will work it out 
Also by applying the same principle there is a spot in the Alliance base that allows you to do similar things.
GOOD LUCK!!!
8 Sept, 06 - Added Wall Jumping Guide.
10 Sept, 06 - Added EPL Tower exploit
10 Sept, 06 - Added Behind Horde & Alliance Flag Pics