KBPiano will turn your computer into a piano. Just press the keyboard's keys and you'll hear sounds coming out your speaker. You can configure the program to play chords by pressing just a key (configured automatically when you create a new file). Supports 15 channels, and realtime mixing, so you can create professional quality midi files.
It is very easy to learn and use. If you want to record your own songs, give KBPiano a try !