The Mercado Lonja del Barranco is a relatively-new gourmet market on the banks of the Guadalquivir in Seville; think of it as Seville's answer to the famous Mercado de San Miguel in Madrid. The Lonja del Barranco Market is rather small but it has everything you need for a tasty evening: several bars specializing in beers, Spanish wines, and Andalusian favorites like sherry ("vino de jerez") and rebujitos (a local spritzer made with sherry and 7-up), and 10 or 12 stands selling a greatest-hits of southern Spanish cuisine: fresh seafood, Spanish ham and charcuterie, cheeses, olvies, fried fish, grilled meats, and tostas (small slices of bread topped with a variety of tasty treats like tuna with pesto, Spanish blood sausage with apple compote, and the like).
What really sets the Lonja del Barranco market apart, though, is that it has a terrace overlooking the river and the traditional Triana neighborhood. I'd suggest heading there around 7 or 8 in the evening, grabbing a refrshing glass of Manzanilla sherry and a few tostas and sitting out on the terrace to enjoy the sunset and the lively atmosphere around the river as the sun goes down. The prices are reasonable for this sort of place, especially for the drinks which don't usually rise above 2.00 or 2.50 euros.
If you're looking for a nice place for pre-dinner drinks and appetizers, Mercado Lonja del Barranco is a solid choice.