Here's a ranked listing of Fonts.com Web Fonts' top 100 most used Web fonts for April 2012:

Neue Helvetica

Trade Gothic

DIN Next

Futura

Frutiger

Avenir

Helvetica

ITC Avant Garde Gothic

Trade Gothic Next

Neue Frutiger

Gill Sans

Univers

New Century Schoolbook

DIN 1451

PMN Caecilia

ITC Lubalin Graph

Neo Sans

Avenir Next

Linotype Didot

Frutiger Next

Monotype News Gothic

Slate

Futura T

VAG Rounded

Linotype Univers

Harmonia Sans

Garamond 3

Camphor

Gothic

Heisei Kaku Gothic

Bauer Bodoni

Soho

Rockwell

Laurentian

Soho Gothic

Eurostile LT

Glypha

News Gothic

Plantin

ITC Franklin Gothic

Sackers Gothic

Egyptian Slate

Clarendon

Century Gothic

Cachet

FB Han Gothic

Ocean Sans

Plate Gothic MT

ITC Officina Sans

Monotype Grotesque

MYuppy

Gill Sans Infant

Charlotte Sans

Neue Helvetica eText

Bell

ITC American Typewriter

Arial

ITC Blair

ITC Franklin

Bembo

Optima

Monotype Modern

Calvert

Eurostile Next

Wiesbaden Swing

Aachen

ITC Garamond

Neuzeit Office

Mitra

Baskerville

Amasis

Abadi

Adelle

Neo Tech

ITC Kabel

Serifa

ITC Conduit

Monotype Garamond

Walbaum

Klint

ITC Officina Serif

Impact

ITC Bailey Sans

URW Franklin Gothic

Bell Centennial

Akko

ITC Stone Sans

ITC Caslon No. 224

Tahoma

Basic Commercial

Museo

Linotype Feltpen

Rotis Sans Serif

Siseriff

Figural

Droid Sans

Mundo Sans

TB Kaku Gothic

Times

Bodoni LT