There are hundreds of apps out there that let you trigger a handful of preset sound effects. But you don't need an app to have fun with sound effects. With some free software and any Mac or PC, you can make a custom sound board that will make apps seem like kid toys.
To see a video version of this tutorial, visit CNET TV.
To make this happen, download a free program called Soundplant. Open it up and you'll see a virtual keyboard that you can drag and drop sounds on or load individually. These can be short sounds, loops, or full songs, but if you want to play anything other than AIF and WAV files, you'll need to pay for a registered version.
Once you've mapped a sound to a key, you just press the key and your computer plays the sound. If it's a long sound, you can kill it by holding the shift key and pressing the button again. If you dig a little deeper, you can adjust volume, panning, loop, and launch settings for each key.