barcelona
+1
but for the selfish reason that I have free accomodation there due to the missus sister and a few friends living there
Great city though, great weather in the Autumn (when the Euro Champs usually held) and plenty of cheap accomodation to be had at that time of year. Nice big casino & hotel by the waterfront and i"m sure there"s another in the centre of barcelona too. Some really good places to see in the off days: Nou Camp, Gaudi buildings/park, Sagrada Familia, Olympic Stadium, etc etc...