You can also add to the list AKA Sushi Bar (our current favourite). You can find this at Max Henriquez Urena #50 esq. Lope de Vega.
We had a wonderful lunch yesterday at Vesuvio on Ave. George Washington.
Other favourites already mentioned are EAT, Mitre, Marocha and Sophias.
If you are looking for really good Italian food, I would recommend Le Fettucine at Ave. Nunez de Caceres #593 just north of Gustavo Ricart (next to Pizza Hut). It is not 'posh' - more like the little italian restaurants you find in Sicily. Owned by an italian family -the food is fabulous and the price even better.
Restaurant "Sully" is a wonderful little seafood place (Ave. Charles Sumner # 19 esq. Calle Los Caobas, Los Prados). The decor is very 70's. The staff are all dressed in dinner suits with bow ties. There lobster is to die for and very reasonably priced.