Easiest language

Esperanto.

http://en.wikipedia.org/wiki/Esperanto

For a free software course (multilingual) see http://www.cursodeesperanto.com.br/bazo/index.html?en

Most people find Italian and Spanish easy to learn. But I agree, Esperanto is probably the easiest, but keep in mind that it was

It's a very subjective matter, indeed.

For what it's worth, I found Spanish to be somewhat easier than Latin, German, or French. Spanish grammar is less complicated, there are not many irregular verbs, and the total vocabulary is smaller than those of the other languages I mention. 

Having said that, I should add that I have a better command of French than of any of the other languages I've studied, because I've lived and worked in French for a number of years, developing much greater fluency than I ever had with the others.  

The Pimsleur approach is so effective because it is based on tried and tested techniques and principles that have proved to enable rapid and successful language learning.

The unique audio method allows the listener to learn pronunciation, vocabulary and grammar without repetitive rote learning, in a similar way to how we acquired our native language components. An effective spanish downloadable audio book.