Play two different notes with buttons.

/* 
  two_note_keyboard
*/

int speaker = 9;
int button1 = 2;
int button2 = 4;
int note1 = 262;
int note2 = 294;
int value1, value2;

void setup() {
  pinMode(speaker, OUTPUT);
  pinMode(button1, INPUT);
  pinMode(button2, INPUT);
}

void loop() {
  value1 = digitalRead(button1);
  value2 = digitalRead(button2);
  while (value1 == HIGH || value2 == HIGH) {  
    while (value1 == HIGH) {
      tone(speaker, note1, 20);
      value1 = digitalRead(button1);
    } 
    while (value2 == HIGH) {
      tone(speaker, note2, 20);
      value2 = digitalRead(button2);
    }
  }
}