This SMD FM transmitter has an operating frequency of about 80 to 115MHz. Under reasonable circumstances you will be able to receive its signal at a distance of about 200 meters. Although it is low-power, it might be illegal in your part of the planet.
Here's the circuit:
Depending on the electret microphone you use, you might have to tweek R4 to set the gain of the pre-amplifier. Depending on the Q of the LC-part (usually not very good when using off-the-shelf SMD parts) you may also have to re-bias the end stage of the circuit.
You can download the PCB design here (only 2.5Kb). It's a double-sided PCB in CorelDraw 3.0 format (zip compressed).