Enhancing Your Special Moves
Along with Special Moves, every character in Street Fighter IV also has EX Special Moves. Generally, these are enhanced versions of existing Special Moves performed by doing the Special Move code but finishing it with two buttons instead of one.
For example, to do a Hadoken, Ryu presses Down, Offensive Crouch, Towards on the controller and hits one Punch button. But to perform an EX Hadoken, you would press Down, Offensive Crouch, Towards on the controller and hit any two Punch buttons at the same time. The EX Hadoken is faster, hits twice, and knocks down on hit compared to the regular Hadoken.
The cost of performing an EX Special Move is 1 Block of your Super Meter. There is one exception to this rule, however: Seth's EX Tanden Engine. Apparently, Capcom thought the move too powerful to cost only one Block of Super Meter.
Outside of costing a Block of Super Meter, EX Special Moves retain all properties of regular Special Moves. EX Special Moves also come in two forms. And although it's impossible to cancel an EX Special Move into a Super (that would require more Super Meter than you are allowed), it technically is allowed (you can see this for yourself in Training Mode by setting the Super Meter to infinite).
EX-Less Specials
Some Special Moves do not have EX versions of them, such as Zangief's Double Lariat and Dhalsim's Yoga Teleport.