RS Components are an electronic part supplier who sell a large range of components and tools related to electronics. I have always had a good experience buying from them. They are also a stockist of Arduino boards and accessories, catering not only for the electronics industry but also for the electronics hobbyist and home user.
An op-amp is used as an oscillator in this LED flasher circuit. This is another circuit that can easily be built on an electronic breadboard by beginners in electronics. Click the above link for the circuit diagram.
This circuit uses a 555 timer IC and produces a fixed frequency audible tone that is played through a loudspeaker. No amplifier is necessary as the 555 puts out a signal of high enough amplitude. The circuit is easy to build for beginners in electronics and can be built on an electronic breadboard. Click the above link to find the circuit diagram.