For women (or whomever), I find decorative fans to be a VERY nice gift. The come in all qualities and prices, some hand-painted and some by machine, some plastic and some wood, some come with a stand/support and some without. You'll find these in almost any tourist shop but I got mine for my mom in Madrid in the north (in)side of the Plaza Mayor. I'm sure they have more in Andalucía.
For women, it's tougher, I think. If an older man, a Spanish hat/"gorra" can be an interesting gift - IF that man wears hats, that is. It's SOMETHING like - but not exactly - a french beret. I got my father one in Madrid in a hat shop on the north (in)side of the Plaza Mayor and he loves it. All hats are SIZED, though, so come prepared.
For more trinket-like gifts, I like to give keychains with Madrid or Spanish monuments on them. These, you can get in any giftshop in Spain but in Madrid you'll find them either on the west side of the Plaza Mayor or just at the bottom of the steps of the southwest corner of the Plaza Mayor.
Also good gifts are cans of green, Spanish olives stuffed with anchovies - A MADRIDMAN FAVORITE!!!!!!!!!. These are relatively cheap in any grocery (but more expensive at El Corte Inglés, of course), about 0.70 - 0.90 Euros. I got some at the MaxCoop for about that price but bought some more at Madrid Barajas Airport for about twice to thrice the price (hey, that was a rhyme!). Bags of almonds can be cheap, bottles of olive oil from the grocery are CHEAP CHEAP CHEAP - AS OPPOSED to those at Barajas Airport but those at the airport are often packaged in a nice, see-through gift box.
Too bad you can't take back an entire Tortilla de Patatas. :p
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