Badger reports on an interaction she had with some classmates on the relative vocabularies of various languages. My reply, not necessarily reality-based:
(1) I've heard the same thing you have, that English is a happy borrower, nay ransacker, of vocabulary and by being a language of world conquest for a few hundred years has sucked up a lot of words.
(2) One should nevertheless not assume that just because the Academie de la Snootologie for a particular language hasn't sanctioned words, they aren't part of the real language anyway. Spanish in particular, between the Moors on the one hand and even more contact than English with indigenous American languages on the other, could possibly give English a run for its money whatever the Academía Española says.
(3) This all depends on how you define the boundaries of a "language". Do local dialects count? Even geographically dispersed or mutually incomprehensible ones?
(4) Finally, any competent debunker of the "Eskimo Words for Snow" myth would point out that lots of languages don't even have distinct "words" as we use the term, so counting the words in those languages is like counting the toes on a fish.
Clearing out a few other language links I've been hoarding:
(Patrick Hall's Linguablogs list is down this morning. Anybody else had problems with it? Has he been updating it? I haven't checked lately.)