The standard exhausts for both a Lambretta and a Vespa are very basic and don't do an awful lot to help the motor produce what it is capable of. The exhaust is also the easiest part to bolt on to your bike and gets the most bang for the buck. Many companies have done research into exhausts for scoots and they range greatly. Some pipes give a great spread of power over the RPMs but others only hit between a specific RPM range. The following section doesn't really rate exhaust systems but does note how to install the most common ones.

Above is a shot of a standard Vespa P200E exhaust that fell apart...not exactly cutting edge but it does the job until you start messing with your engine. Then it becomes a restriction to the possible performance.