Alfa Romeo Guilietta, Mito, 147 and Brera would all be worth a look and the Alfa JTD (Diesel) engine is a little cracker.
The BMW X3 (and possibly X1, although these are newer and therefore not as cheap yet) might also be worth a look. Not exactly 'exciting' to drive but as good as a regular hatchback rather than as bad as a regular SUV.
The Qashqai isn't a bad choice and also the new Juke although I've no idea where the prices of these are at the moment.
The Citroen DS3 is an option as it's a cracking car to look at, not something you see everyday and again, the diesel engine is the one to go for.
Sticking with the French, a Renault Megane could be good. Make sure you go for a new model Coupe though, or at the very least, a 3-door. Or for something more interesting you will probably find an old model Cabriolet that's in budget.
Thinking about Cabriolets, you could try a VW Eos. The folding hard top offers more comfort and security and all round, they're not a bad car.
Changing tack slightly is the Audi TT. While the diesel TT might be out of your price range (again, a bit too recent) it could be worth looking at a petrol one.
Above all.... PLEASE PLEASE PLEASE don't be boring. Every man and his dog consider a Golf or a Focus.... buying a Renault (E)Fluence simply show's you've given up on life... and a Toyota Auris is just beige....
(There is of course option B.... spend 15k on something really really interesting and use the remaining 5k to keep it on the road.....
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Just a thought....... )