What comes next...

quadrillion (I think)

http://www.jimloy.com/math/billion.htm

3 thousand thousand
6 million million
9 billion 1000 million (1 milliard)
12 trillion billion
15 quadrillion 1000 billion
18 quintillion trillion
21 sextillion 1000 trillion
24 septillion quadrillion
27 octillion 1000 quadrillion
30 nonillion quintillion
33 decillion 1000 quintillion
36 undecillion sextillion
39 duodecillion 1000 sextillion
42 tredecillion septillion
45 quattuordecillion 1000 septillion
48 quindecillion octillion
51 sexdecillion 1000 octillion
54 septendecillion nonillion
57 octodecillion 1000 nonillion
60 novemdecillion decillion
63 vigintillion 1000 decillion

centillion

Googol - The number 10 raised to the power 100 (10100), written out as the numeral 1 followed by 100 zeros.

Googolplex: The number 10 raised to the power googol, written out as the numeral 1 followed by 10^(100 zeros.)