Ping

Ping is the sound effect most often associated with the Home Run Bat. It also is used for several powerful attacks. In Melee, it is possible to hit with the bat in a way that DOESN'T make a Ping, known as a No-Ping Hit. This will have more knockback than a normal hit.

In Super Smash Bros.
In the first game, the sound effects were vague and generic variations that might be described as "WHOCK" or "POM". The actual Ping, however, is very distinct. It is also used in the opening cutscene. The attacks that Ping are:
 * Home run Bat
 * Ness's Forward Smash
 * Luigi's Fire Jump Punch
 * Jigglypuff's Rest

In Super Smash Bros. Melee
Here, the attacks were given more realistic and varied sound affects. There was a single addition to the previous Ping attacks:
 * Freezie was a bit unique in that it had a very slightly different Ping, and it made the sound whether it hit an opponent or not.

In Super Smash Bros Brawl
Brawl has changed sound effects for certain items and attacks.
 * Freezie no longer Pings, instead using the classic sound effect from its appearance in Mario Bros.
 * Ness's Forward Smash has been changed to sound more wooden, and "CRACK"s like a real bat.
 * Luigi's Taunt now Pings also, most likely to make it more noticeable, since the Bonuses no longer indicate when one has connected successfully. It's also a joke in that most Ping attacks are excessively powerful, but the taunt only does 2% damage and moderate fixed knockback.