Small city cars (used) to consider

If you are living within a city and most of your commutes are within, then look for a small but safe car as your primary car.
What fuel?
Since most of the trips will be shorter, petrol/gasoline engines will be better. Increased engine shutdowns will have adverse effect on a turbo charged diesel engine
.
List of 10 small, reliable and safe used cars (author's opinion) that you can fetch in a budget of 6 - 10 thousand euros:

1. Mazda 2 (>2008 models)
   - ENCAP 5 star; fun to drive, Mazda reliability; re-sale value
2. VW Up, Skoda Citigo, Seat Mii
   - all same in different skin; safe city car; efficient
3. VW Polo, Skoda Fabia, Seat Ibiza
   - safetly, reliable (newer engines), re-sale value)
4. Ford Fiesta hatchback
   - safe, fun to drive, plenty, re-sale value
5. Hyundai i20
6. Suzuki Swift
7. Opel Corsa
8. Fiat Grande Punto
9. Chevrolet new Aveo (!!Chevrolet is planning to stop their operation in Europe by 2015)
10. Renault Clio