How to say "No"

I was talking to someone from  the Netherlands yesterday, about learning languages.  Without getting into the discussion on whether or not the English language has the largest  number of words (common words? what is a word? whose count?), my friend said he loved the diversity of English as a language, its nuances, its shades of meaning.

He had already lived for a year in London (and a fluent English speaker) when his company insisted that he attended English lessons, three days a week, two hours per lesson.  The first two weeks were concerned solely with how to say no, and how to interpret variations on saying no.  He explained to me that in Dutch, if they want to say "no", they say "nee", but you can't depend on an English speaker to do that:

Would you like a drink?

I wouldn't.
Not at the moment.
Perhaps later.
A nice idea but....
I'd rather not.
Thank you, but....

Are you coming to the xxx ?

Possibly.
I have a lot on at the moment.
I'll have to see if I can fit it in.
Could you ask me closer to the time?
It clashes with....
It certainly sounds interesting...
I'd love to but....

And so on.  the idea fascinates me.  How many ways are there to say no?