Some of the drills that I like in my curriculum are the following:
TED (Threat envelope drill)
Used in conjuction with stance training to help learn distancing. Basically two individuals square off and as one moves the other reacts to make sure the distance is JUST far enough out that the opponent cannot hit them without a major step forward. Later on when attacks are added, the reaction to an attack is also as such so that the attack is just falls short so that a counter can be made effectively.
Man Sau (asking hands)
GTG (Guarding the gates)
To gain an understanding of the 6 gates, I use this to show the idea of taking the space of the area that is being attacked. The specific technique doesn't matter as much as the idea of taking away the space in the gate that is being attacked.
Keeping the Jung Sin (retaining the centerline / attacking line)
5 point drill (not a sparring drill, but rather for conditioning)
This is something I like to do simply to help build conditioning in the forearms and wrists. Basically each person uses Noi gaan sau, Tan sau, Gaan sau, Jaam sau, and wu sao...at the same time with opposite arms. This conditions the forearms while practicing sao fot.
MTH / ID (Meeting the hands and interception drill)
This drill is a two step process. The goal is to first get the student used to seeing punchines / strikes coming at him in fast and continous succession...not all straight punches either. Anything goes. The student will react to these by defending in free form (blocking, deflecting, covering, redirecting, etc). Later, with the attacker using the same rythym, the defender will infuse a counter strike on the half beat while still defending (and not getting hit).
Don chi sao, and its variations
Poon sao / gor sao / lok sao
Gan gerk / chi gerk
Progressive sparring / limited sparring
Progressive sparring is similar to the 1-2-3 step sparring you'd see in many martial arts styles. Prearranged or spontaneous. This is also where you'd see things like learning to see when and how to stop hit. Generally it weens the individual into the full-out continuous sparring. Limited sparring is where one individual must work a specific skillset or range of fighting, for example one person is working kicks and the other is working kick defenses against someone that's actually trying to kick them.
Free sparring
Anything goes, done at varying levels and intensities, gear, no-gear, as the students skill permits