Ordinary light switches should be do-able unless they have so much resistance that it wouldn't pass the smaller direct current that the Arduino puts out.
However, you won't be able to connect 30 light switches to an Uno or Leonardo without additional hardware, since those boards don't have 30 pins you can attach things to. The Mega and Due do have 54 digital pins. Bear in that 30 regular light switches will take up a large amount of room, plus the amount of wires, etc. you will need to hook all of these up.
If I were doing it, I would think about alternative inputs. Perhaps a potentiometer or a rotary encoder that the user could have one control and dial to the 30 different inputs. Or perhaps 3 4x4 membrane keyboards that would give you 36 keys. Or perhaps a USB host shield and plug in a USB keyboard, and each key would be a different sound.
If you still want to do something like light switches, consider getting toggle switches that are much smaller than light switches, and can fit in breadboards, such as: Search Results for toggle switch - SparkFun Electronics.
You need to figure out what should be done, if the user presses 2 or more buttons at the same time.
In order to play sounds you will need a sound shield or something similar. With AVR based arduinos, you probably won't have enough memory to hold 30 different sound samples, and you will need to think about having a SD card to hold the sounds. I think with the DUE that was officially announced today, that is less of an issue. Here is the sparcfun audio shield: SparkFun MP3 Player Shield - DEV-12660 - SparkFun Electronics.
I would recommend, starting small, and concentrate on having only 2-3 keys at first, and then as you scale up, you may need to go to beefier hardware to handle that many inputs.