There were a couple of items on this morning's Today programme on Radio 4 about how the pronunciation of certain words is changing (listen here for another week). Younger people are far more likely to rhyme says with days and pronounce ate as eight than are their parents (whose pronunciation rhymes with fez and net), and to stress the o of kilometre and the second o of controversy, words which older people are more likely to stress on the first syllable. Other words whose pronunciation is changing, according to John Wells, Emeritus Professor of Phonetics at UCL, include poor, tour, sure, harass, garage and create. Aitch, the 8th letter of the alphabet, is increasingly being pronounced haitch these days.
There is nothing new about the pronunciation of words changing. In a 1928 guide to pronunciation issued by the BBC the final syllable of pristine rhymed with line, combat sounded more like cumbat, respite was stressed on the first syllable and the second syllable sounded like spit and finance was stressed on the final syllable. There are more examples in this article.
The British Library is compiling an archive of different, modern pronunciations and visitors to a forthcoming exhibition on the English language can record their voices reading a set passage from the popular children's book Mr Tickle, which has been slightly adapted to include words whose pronunciation is known to be in flux.
More on this subject in this BBC article.