Names of Polygons:

N - N-Gon
1 - Monogon
2 - Digon
3 - Trigon, Triangle
4 - Tetragon, Quadrilateral
5 - Pentagon
6 - Hexagon
7 - Heptagon
8 - Octagon
9 - Nonagon, Enneagon
10 - Decagon
11 - Hendecagon, Undecagon
12 - Dodecagon
13 - Triskagon, Triskaidecagon
14 - Tratagon, Tetradecagon, Tetrakaidecagon
15 - Pentadecagon, Pentakaidecagon
16 - Hexadecagon, Hexakaidecagon
17 - Heptakaidecagon
18 - Octakaidecagon
19 - Enneakaidecagon
20 - Icosagon
30 - Triacontagon
40 - Tetracontagon
50 - Pentacontagon
60 - Hexacontagon
70 - Heptacontagon
80 - Octacontagon
90 - Enneacontagon
100 - Hectogon, Hecatontagon
1000 - Chiliagon
10000 - Myriagon (from myriad, meaning 10,000)

Note: "kai" means "and"

Note: These have both Greek and Latin prefixes, if anyone has anything to add, please /msg Vos.