Again your best one stop check is with a travel agent in the country you intend to visit.
For prices in general: Jan-Early March (except for the week before and after Easter/Passover), Late Aug through early November are the cheapest travel dates anywhere, because it's when the fewest number of American's travel.
But you also have to check on any in-country major holidays, which will increase return travel for citizens of the country which may result in a decrease in availabiity of hotel rooms and a corresponding increase in prices.
http://www.weather.com/outlook/travel/vacationplanner/vacationclimatology/monthly/RPXX0017
Go to
www.weather.com to check out the monthly temps and rainfall for any country. The worst time there will be the cheapest time to travel. Depending how far in advance you book, the ten day forecast on most weather sites will give you an idea of what to expect for a short term stay. Contacting Dive or ski or surf web sites in the country are also an excellent source for when is the best time to travel, ddepending on what your criteria is. Another good source is checking-in any ex-pat websites for the country you intend to visit.