Player gets stuck on collision when jumping up a platform.

This is a bit late :), but I had the same issue.

Just after the line that reads horizontal axis

 float move = Input.GetAxis ("Horizontal");

added the following line

 if (!grounded && Mathf.Abs(move) > 0.01f) return;

So, if the player is not grounded and he is moving then just return and do not execute any movement code. Again, I assume your are using tutorial script. So, the whole FixedUpdate looks like this

 void FixedUpdate ()
 {
     grounded = Physics2D.OverlapCircle (groundCheck.position, groundedRadius, whatIsGround);
 
     anim.SetBool ("Ground", grounded);
 
     anim.SetFloat ("VerticalSpeed", rigidbody2D.velocity.y);
 
     float move = Input.GetAxis ("Horizontal");
 
     //prevents the player from getting stuck into platform
     if (!grounded && Mathf.Abs(move) > 0.01f) return;
 
     anim.SetFloat ("Speed", Mathf.Abs (move));
 
     rigidbody2D.velocity = new Vector2 (move * maxSpeed, rigidbody2D.velocity.y);
 
     if (move > 0 && !isFacingRight)
         Flip ();
     else if (move < 0 && isFacingRight)
         Flip ();
 }

If you are using the tutorial script, just add this 'if' before this line:

 if (grounded)
     rigidbody2D.velocity = new Vector2(move * maxSpeed, rigidbody2D.velocity.y);

There is new unity component called platform Effector 2D that will allow you to do that: more info here: http://docs.unity3d.com/Manual/class-PlatformEffector2D.html