Here's a ranked listing of Fonts.com Web Fonts' top 100 most used Web fonts for July 2013:

Neue Helvetica

Trade Gothic

Proxima Nova

Futura

Gill Sans

Helvetica

Avenir

Univers

DIN Next

Avenir Next

Neue Frutiger

Frutiger

Linotype Univers

ITC Avant Garde Gothic

Trade Gothic Next

Frutiger Next

Humanist 777

ITC Franklin Gothic

Arial

Adobe Caslon

Century Gothic

Museo Sans

Baskerville Classico

Optima

Univers Next

Bembo

Linotype Didot

Neo Sans

News Gothic

Agilita

Soho

VAG Rounded

PMN Caecilia

Rockwell

Myriad

Monotype News Gothic

Bodoni LT

DIN 1451

ITC Lubalin Graph

Brandon Grotesque

Helvetica Monospaced

Gill Sans Infant

Futura T

ITC Century

News Gothic No.2

Trade Gothic Next Soft Rounded

ITC Garamond

ITC Officina Sans

Twentieth Century

Soho Gothic

Aachen

Sabon

New Century Schoolbook

ITC Conduit

Abadi

Neue Haas Grotesk

Adelle

Neue Helvetica eText

Eurostile LT

Bembo Infant MT

Letter Gothic

Times

Corporate S

Memo

Eurostile Next

Harmonia Sans

Bauer Bodoni

Sackers Gothic

Frutiger Serif

Calibri

Laurentian

Franklin Gothic

ITC Franklin

Palatino

Camphor

Helvetica World

ITC Fenice

Neue Helvetica Arabic

Adobe Garamond

Akko

Slate

Museo Slab

Klint

Heisei Kaku Gothic

Strayhorn

Novecento

Garamond 3

Clarendon

New Caledonia

Swiss 721

M Sung PRC

Minion

Ascender Serif

Yakout

Monotype Baskerville

Plantin

Thud

ITC Officina Serif

Effra

Albany