Here are a few I have found very useful in the past:
Jump Reverse Side Kick- Sparring stance, you jump and turn your body towards the oponant... Chambering the back leg for a side kick. When you turn nearly 180degrees around, throw out that chambered leg. Use this when your oponant has commited himself to a charge. Practice this as a close-in technique. If done right, they'll never expect a jump kick while that close to them.
Twist kick- each are facing oposite directions (closed stance). When nice and close, they'll be trying to punch. Block/cover-up and twist kick the front foot and connect it to the back of their head. Its a blind spot move.
360 degree jump reverse side kick- like the jump reverse, but this time the kick comes from the front leg after spinning 360 degrees around. Leaping at them and spinning, they'll most likely guard the head.. however, aim for the chest/stomach.
Jump side/side- This is a simple jump side kick, however, when you land (and the kick was probably blocked) DO NOT PUT THE KICKING LEG DOWN. Keep it up as you land on one foot and quickly side kick it again (no jump this time). Oponant will probably be trying to throw a punch or two, thinking you're in the landing process and they'll end up runing into the side kick.
Hand Techniques- Being TKD has a lot of kicking... and the fact that too many rely on kicking for the big points in the ring... I have found that getting close in and using blocking/striking with the hands has done well. Work on bouncing in and out of hands range until you feel quick enough... before you know it, you'll be able to score a punch within the same distance as a kick. No one ever expects that to happen. Not even the judges, so careful that they "see" the technique.
Hope this helps some!