This LilyPad switch will give you momentary contact in your circuit (closed when pushed and open when released.) It is small enough to be discrete, and it features smooth edges all around.
The LilyPad is a collection of electronic circuits and accessories for Arduino. Most components feature connecting pads so you can sew them into clothing and are even washable! Various input, output, power, and sensor boards are available.
You can also use LilyPad components, like this switch, for science demos and classroom projects by connecting them with alligator clips cables.