Is it Web site or website?
Since the World Wide Web is a proper noun, we use initial upper-case letters, as we would with your surname, for example.
As for writing ‘Web site’ as one word, it is true that this is seen a great deal, but then, so is the spelling ‘recieve’ which is just plain wrong!
Since this is a site on the World Wide Web, we are really using a shortened version of ‘a site on the World Wide Web’ or ‘a World Wide Web site’.
Just as you would not write ‘buildingsite’ or ‘constructionsite’, I would suggest showing the derivation of this phrase by retaining it as two words, coming from ‘a World Wide Web site’.
Incidentally, in any other context, the word ‘worldwide’ should always be one word, with no hyphen, just like ‘nationwide’.