What areas of the world are you considering? I've done a lot of research into this subject, and was actually accepted to a program in France (had to back out due to scheduling conflicts with university schedule I was attending in France). I've got info on non-profit/NGO organizations, teaching through the government, private language institutes, etc.
Hey Wicked - As a good starting point for your research, check out http://www.teachabroad.com/search.cfm.
Another great option: www.worldteach.org
Also look at www.idealist.org. You can search under "volunteer positions" and then specify the country and type of opportunity you're looking for.
As for Spain, I haven't seen many opportunities, though I did come across one recently that's a combined master's in Spanish and English conversation teacher program. Basically you pay for your living and tuition expenses by teaching 10-15 hours of English conversation a week. Pretty darn good deal if you ask me. If you're interested in finding out more, let me know and I'll dig up the info. But as far as just straight teaching positions, you kind of have to go and then just cross your fingers. You would want to get a TOEFL beforehand if you're planning on teaching English.
Finally, I know you didn't mention Eastern Europe, but there is an AWESOME program in Hungary that I've been salivating over for the past few years. You can teach for either 6 months or a year, and it's through the government. You're provided housing and a salary.
If you're a credentialed teacher, there are lots of other opportunities. I would do a google search for American schools in whatever country you're interested in. Typically you'd be teaching the children of diplomats not only from the US, but the host country and others as well.
Please feel free to ask if you have any questions!!!