• Tunnel Glitch
You'll need the riot shield from the diner for this glitch.
In the tunnel as you come in (bus direction), on the right side there is the cat walk like path. Using the riot shields, you can place it on either side in the corners. Doing this, the zombies will get stuck outside of the rails.
• Power Plant Glitch
Not sure the requirements of this, but someone else can add on to this.
All I know is that you have to croutch down on the lower level in the upper room near the fall in the ground, closest to the door to the power switch side.
Hopefully my directions are understandably without a vivid scene, but you can also use this thread to post your found glitches.