One suitable song, judging by the way some students seem to forget the basics, is this classic:
However, over the years I have collected a large amount of videos, some of which I use in my lessons, which are fun and from which you can also get some ideas of what to talk about with this topic. Here is a selection:
The History of English in 10 minutes (a very useful & funny overview of how English developed):
The German Coastguard (a funny example of why it is hard for foreigners, especially Germans, to use the 'th' sound):
Inspector Clouseau -(the problems the French have!):
The Super Interpreter (how other languages sound to the English!):
Alex Rawlings - (a young man who has learnt 11 different languages!):
Pronunciation Poem (to help with some common mistakes):
How German sounds compared to other languages (great fun, and good to compare the other languages!):
And last, but not least, if you feel that (as a Czech) your English is not very good, then this guy will make you feel MUCH better ;-)