If you want a dining area that is ripe with energy, great Spanish architecture and lined with tapas establishments, then your first choice should be Cava Baja. Located near Plaza Mayor in the La Latina neighborhood, this street is chock full of some of the best tapas bars in Madrid, coming alive with strolling travelers and locals as evening progresses. Honestly, there are dozens, serving not only an incredible range of tapas (pintxos) but also beer, wine and cocktails. Casa Lucio and La Chata are locally famous and have deserved reputations, while places like Madrileno, Lamiak and Taberna Txakolina (the connoisseur's temple of tapas) are quite often packed and will cost you less.
Get out of Centro and get to Cava Baja; there may be no cooler place to combine drinks and snacks in all of Madrid.