If you regularly order items from Amazon as I do and you live in Spain, check out their Spanish web site. Most of the items on the British site are available from the Spanish site and the prices are normally similar (the only exceptions are items from Amazon market place traders).
On the Spanish site you do have to pay for delivery though – there are three rates:
9.99 euros if you want the items next day – normally sent by courier which could be DHL UPS or SUER.
5.99 euros if you want the items within 2 to 3 working days
2.99 euros if you are prepared to wait up to 5 days
In fact, Amazon use Correos for the standard rate and normally post items out the same day you order them from Madrid. Invariably, Correos then deliver the items (signed for) the next day.
It used to be the case that the UK site would deliver items over £25 to Spain free of charge using MRW but not any more.
Is there a catch – well in most cases the description in English will find you the items on the Spanish site but there are some cases where you need to know the language. The instructions for the items might be in Spanish. However, for most items they are in several languages and of course any plugs for electrical items will be euro 2 pin.