Some helpful technique videos:

Freestyle

Michael Phelps - https://www.youtube.com/watch?v=ax77_hHq9Dc

Ian Thorpe - https://www.youtube.com/watch?v=-8egC7PbOME

Notice how high he gets his elbow up on the catch part of his pull, and how large his kick amplitude is

Brent Hayden flip turn - https://www.youtube.com/watch?v=sZ3wHa82zAQ

Notice how he enters the turn with his last pull, gets into streamline right away, and pushes off at a 45 degree angle

Brent Hayden start - https://www.youtube.com/watch?v=IyhlYVYkvzo

Watch his neutral body position (not slingshot start) and how he pulls off the blocks with his hands, entering the air with his shoulders followed by his hips and feet. In an ideal start, the whole body should enter through the same 'hole' in the water, which is exactly what he does. Brent Hayden has his start down to a science and enters the water at a 37.5 degree angle every dive.

Backstroke

Ryan Lochte - https://www.youtube.com/watch?v=7CmM_Z3Zt5U

Aaron Peirsol - https://www.youtube.com/watch?v=UpLr5YwXKKg

Breaststroke

Kosuke Kitajima - https://www.youtube.com/watch?v=8Dz6CtXNG_w

​Watch how fast he is through the insweep part of the pull and how he gets into streamline on every stroke

https://www.youtube.com/watch?v=_ofDYZ8SIC

​On the forward angle, notice how wide his feet are turned out on the kick. Knees are kept together when the legs are being pulled back, and don't come apart until the feet circle around

Butterfly

Michael Phelps - https://www.youtube.com/watch?v=f5iURg-jv0Y

​Watch how low his head is on breathing and how high his elbow is on the catch.