Installed a new head unit today. The Pioneer DEH-2950MP produces a reasonably punchy and clear sound. Adding a sub in future would probably make it sound even better. The downside of this unit is that it cannot interface with the original Peugeot 206 steering wheel stalk control.
To avoid cutting the original Peugeot male ISO connectors, a female ISO connector is mated with it. The female wires are connected to the wires on the Pioneer connector. A custom made harness can also be bought online, but I chose to make my own connections.
Be careful with the yellow (permanent live)(A7) and red (ignition)(A6) wires, as mixing them up can fry the headunit and/or the car's electronics.
The radio antenna socket of the headunit requires a connector that is different to the original Peugeot connector. A suitable ISO to DIN adapter is required.
The adapter can be bought from ebay: http://www.ebay.co.uk/itm/CAR-AERIAL-ANTENNA-ADAPTOR-ADAPTER-CAR-RADIO-STEREO-ISO-to-DIN-PIONEER-KENWOOD-/291095630674