SPECIAL MOVES

FIREBALL (HADOUKEN) - IN AIR OK

   
QUARTER CIRCLE FORWARD + ATTACK

This is Ryu's fireball attack. .  It can be used in the air. The strength of the attack button used determines the fireball's speed and start-up time.  The fireball can be used for zoning when the opponent is far away.  It also causes a good amount of stun, making it a potent component in combos as well.

 HURRICANE KICK (TATSUMAKI SENPUU-KYAKU) - IN AIR OK

  
QUARTER CIRCLE BACK + ATTACK

The hurricane kick hits multiple times and is useful in combos.  The strength of the attack button used determines the move's start-up, duration, and damage.  The weak attack version hits twice and has the fastest start-up.  The medium attack version hits three times.  The hard attack version hits four times, travels the farthest, does the most damage, and builds the most meter. 

All three versions of the hurricane kick will knock an airborn opponent to the ground.

Can be cancelled into Shinku-Hadoken or Shin-Shoryuken.

Worth noting that if done while airborn, Ryu's hurricane kick will keep a grounded opponent standing, so it's useful in combos if used right at the start of a jump.

DRAGON PUNCH (SHORYUKEN)

   
FORWARD DOWN DOWN-FORWARD + ATTACK

This is Ryu's classic Dragon Punch.  It is an extremely useful anti-air move.  The strength of the attack button used determines the height of the attack and the damage caused.  The weak attack version hits once while the medium and hard attack versions hit twice. It has invulnerability for most of the attack's duration but is unsafe on block and can be punished if used without care.

SLIDING HIGH KICK / DONKEY KICK (JOUDAN SOKUTOU GERI)

   
BACK DOWN DOWN-BACK + ATTACK

Ryu steps and then kicks the opponent.  It can act as a wallbounce, so if you are near a corner you will be able to bounce them off the wall and follow it up with other moves.  You only get one wall-bounce, however, as repeating this move in a combo will not produce the same effect. This move seems to be most useful in combos as it can be punished if used alone.