Idealista.com, the giant Spanish Property portal makes it easy to find Spanish Bank repossession properties.  It lists them all in one place, which saves you hunting them out yourself.  At the current time of writing this blog post, it has just over 35,000 bank repossession properties across Spain.  This includes second hand properties as well as new and almost new properties.  Not every single bank repo property will be on there, but with idealista.com being the market leader, I would say that a good proportion of them will be on there.  Idealista.com is the Spanish equivalent of Rightmove.

A few years back, I recall that this number was over 100,000 available properties.  I guess this reflects the fact that the massive oversupply of properties has been significantly reduced in recent years, with many of the real bargains having already gone.  But there are still some good deals on there.

The link to these bank repossession properties is http://www.idealista.com/pisos-bancos

From that link you can then narrow it down by city/area.

Here are some direct links to some of the more popular areas in Spain:

Alicante province bank repossessions

Almeria province bank repossessions

Balearic Islands bank repossessions

Barcelona bank repossessions

Gran Canaria bank repossessions

Malaga province bank repossessions

Tenerife bank repossessions

Valencia bank repossessions