best bang for buck cars 15k euro or below

It'll be a good while until I can afford to change but I am looking at options for the moment - I think 15k as an upper limit is a good price range however.

Ideally I'd like a car that is cheap to run/tax however has a nice power reserve for overtaking etc.

Currently drive an 05 1.8 petrol mondeo so tax at 550 a year (plus it's 38mpg penchant for fuel) mean that I'll be looking to change to something cheaper to run when I do trade. However, I'd still like some extra power on tap when I need to bang down gears. The mondy has 130bhp and is pretty heavy, if I could get something lighter and/or more powerful and 07+ I'd be delighted.

I'd like to get an auto if possible.

Things I am thinking of that fit the criteria that I like the look of (all the usual suspects)

Golf TDI DSG
Passat TDI DSG
Audi/Seat etc
(^ basically anything in the VAG diesel range with DSG :P - although these are quite common cars?)
Don't like the idea of a 3 series for above reason - maybe a 5 although with just a 520d, power might be a bit weak?
Mercedes C/E class diesel.
Focus Diesel?

Any more I'm missing out on? I'm 26 and I have no family requirements or anything. Tall as well and do a nice bit of motorway cruising (which is where the mondeo comes in to it's own - wish I had cruise control though )