Welcome to the boards Chac!
I can tell you that getting an english teaching job in Spain during the summer time, will be quite difficult as most people are on vacation to enjoy life, which means most people are not in study mode during this time. The school that I taught in during the summer had anywhere from 2 to 6 people per class with only a few classes each day. Empty is what I´m getting at. Come September, it´s business as usual and the places get jam-packed!
You know how you´re walking down the street minding your own business, when all of a sudden you get these flyers handed to you that say "learn english (or italian, german, french, etc...)?" Go to the address on that flyer and speak to the person in charge. Tell them that you are American and that you are good at teaching english. All they have to do is hear the way that you speak, and of course if you seem like a great guy, and tell them that you can start NOW. If they need someone, they´ll hire you.
I did this approach twice and got both jobs. One took longer because they didn´t need anyone at the time. I checked with them later, she checked her notebook and found my number from my previous visit to her, and she said that I can start at the "sister" school tomorrow at another location. I happened to do a follow up check at the right time
I didn´t have a resume, a certificate, a passport with me, nada! Just looked enthusiastic and spoke CLEARLY to her (as opposed to my natural tendency to garble a lot of my words).
Also, I put a free ad in their local very popular classified paper called "Segundomano" (Second hand), for private lessons and had to dish out work to a coule of other teachers that I had met, because I didn´t want that many students. Private lessons pay more.
You don´t need a certificate or anything like that. Just get out there and network.
Go to an Irish pub and meet a lot of english speaking people that might be able to point you in the right direction. heck, the Irish pubs are a great way to start in terms of looking for work too!
Some Hostels do look for workers in exchange for lodging, but you´ll have to find those as you go.
The famous Pink Palace in Greece has a 2 month minimum work program that you might want to look into. Here´s their link The Pink Palace
Also, there is a thread on this forum that discusses bartending as a nice option that can be useful in any country. You should read that thread as it´ll provide more options for you.
Hope it helps and let us know how you´re doing!