Here's a ranked listing of Fonts.com Web Fonts' top 100 most used Web fonts for September 2011:

Avenir® 55 Roman

Futura® Bold

Avenir® 95 Black, Ext.

Neue Helvetica® 55 Roman

Neue Helvetica® 35 Thin

Avenir® 85 Heavy

Univers® 57 Condensed

Neue Helvetica® 75 Bold

Neue Helvetica® 77 Condensed Bold

Garamond 3 Regular

Garamond 3 Italic

Bauer Bodoni® Black Italic

Sackers™ Gothic Heavy

Sackers™ Gothic Medium

Avenir® 65 Medium

Trade Gothic® Condensed Bold #20, Ext.

Avenir® 35 Light

Neue Helvetica® 45 Light

Neue Helvetica® 87 Condensed Heavy

Trade Gothic® Condensed Bold 20

Trade Gothic® Bold

Helvetica® Condensed Bold

Neue Helvetica® 25 Ultra Light

Futura Medium

Neue Helvetica® 57 Condensed

Administer BookItalic

Avenir® 95 Black

Linotype Univers® 620 Condensed Bold

Linotype Didot® Bold

Linotype Didot® Roman

Linotype Univers® 420 Condensed

Linotype Didot® Italic

Neue Helvetica® 67 Condensed Medium

Linotype Univers® 320 Condensed Light, Ext.

Futura® Book

Univers® 47 Condensed Light Oblique, Ext.

Trade Gothic® Roman

Avenir® 45 Book

Futura® Heavy

Futura® Bold Condensed

Futura® Medium Condensed

PMN Caecilia® 75 Bold

PMN Caecilia® 85 Heavy

Neue Helvetica® 45 Light, Ext.

Trade Gothic® Bold 2

PMN Caecilia® 76 Bold Italic

ITC Avant Garde Gothic® Book

Neue Helvetica® 65 Medium

Monotype Grotesque® Condensed

Neue Helvetica® 37 Condensed Thin

Neue Helvetica® 47 Condensed Light

Neue Frutiger® Light

Trade Gothic® Bold, Ext.

Neue Frutiger® Bold

Neue Frutiger® Book

ITC Legacy® Serif Bold Italic

Neue Helvetica® 55 Roman, Ext.

VAG Rounded™ Bold

Rockwell® Bold

Trade Gothic® Condensed 18

Univers® 67 Condensed Bold Oblique

Avenir® 55 Roman, Ext.

Trade Gothic® Extended Bold

Felbridge™ Regular

Neue Helvetica® 77 Condensed Bold, Ext.

Cochin® Roman

Neuzeit® Office Bold

Neuzeit® Office Regular, Ext.

VAG Rounded™ Black

ITC Avant Garde Gothic® Medium

Neue Helvetica® 63 Extended Medium

Neue Helvetica® 53 Extended, Ext.

Frutiger® 65 Bold

Neue Helvetica® 73 Extended Bold, Ext.

DIN Next™ Bold

Frutiger® 55 Roman

Trade Gothic® Bold #2, Ext.

DIN Next™ Regular

ITC Avant Garde Gothic® Bold

VAG Rounded™ Light

Trade Gothic Next Regular

Helvetica® Bold, Ext.

Helvetica® Bold

Trade Gothic® Condensed #18, Ext.

Neue Helvetica® 65 Medium, Ext.

DIN 1451 Engschrift

DIN Next™ Condensed Bold

Frutiger® 45 Light, Ext.

Neo Sans Regular, Ext.

ITC Avant Garde Gothic® Demi

Palatino® Sans Arabic Regular

Avenir® Next Demi

Trade Gothic Next Condensed Bold

Eurostile® Next Regular

Eurostile® Next Extended Regular

Trade Gothic® Light

Eurostile® Next Extended Bold

Eurostile® Next Extended Semibold

Eurostile® Next Semi Bold, Ext.

Gill Sans® Book