What is a good unityscript writing program?

Hello folks, I need a good program I can write all my scripts in. More info:

1)I am only doing unityscript for now. I will later on learn c# but that is much much later

2)I NEED to have like a dictionary thing. Where when I type for instance a key word and a drop box section pops up allowing me to select which one I want. for example: I type in "fun" and then a little menu pops up with everything that begins with "fun" and i choose "function"

That's really it. Thanks guys :)