[Arkcon]

Right. So. For American English at least, and for the truly pedantic nerds among us -- (The applicant for your consideration as the biggest nerd speaking here, ahem) -- the list would go like this:
(Wish I knew how to set the small font like everyone else does)

10^3 thousand
10^6 million,
10^9 billion,
10^12 trillion,
10^15 quadrillion,
10^18 quintillion,
10^21 sextillion,
10^24 septillion,
10^27 octillion,
10^30 nonillion,
10^33 decillion
10^36 undecillion
10^39 dodecillion
Insert - 10^40, number of hydrogen atoms in the universe, we guess (well astrophysicists, not me personally)
10^42 tridecilion
Insert - 10^44, number of seconds in the lifetime of the universe, we guess
10^45 quadecilion
10^48 quintdecillion
10^51 sexdecillion
10^54 septdecillion
10^57 octdecillion
10^60 nondecillion
10^63 eicoillion
Insert - 10^64, energy, in joules, of the Big Bang, we guess, unless someone was there. (anyone?)
10^66 uneicoillion
Insert - Official beginning of numbers that have no meaning to human minds