I just went through a similar exercise last week. I removed the standard unit and replaced it with a JVC KD-BT1 which offers AM/FM radio, MP3/WMA/ACC from CD, USB (thumb drive or disk) and Bluetooth. There's also Bluetooth phone played through the speakers with voice or (using distracting phone book) dialling - all for less than £200. I now have a sound system with a single removable faceplate that offers various sources, without the need for a large CD changer, and a legal hands-free phone.
Apart from the single DIN fascia replacement, I also required an ISO to DIN aerial adaptor. I also opted to add the KT-DB100 DAB receiver which plugs into the CD changer socket. This uses a screen-fitted aerial which is usually provided with the DAB receiver.
Amazingly this all fitted into the space vacated by the original Panda unit. The "empty" slot is above with the DAB received behind it. The sound is good and the Bluetooth convenience superb. If you are confident it's fairly easy to fit once you have worked out where the extra wires (tethered USB, plug in microphone) have to go behind the dashboard. With ISO connections it's otherwise easy to fit and the whole system - including ignition power and display dimmer (activated by the lights) - worked immediately. It took quite a while to read the manual (available from the JVC site) to appreciate all the options and understand how to use them.
Should you decide to install a JVC system or that of another manufacturer, there are plenty of reputable suppliers (many on eBay - they will have a large number of positive feedback references). I bought mine from Budget Car Audio on the Walworth Road - they have a shop if you live locally and don't want to wait for shipping.
In my case, there's no stereo recoding required and when I decide to sell my Panda I'll just swap back to the original system and probably put the JVC system in the next car.
I hope this information is of help.