Seussville: The handler of Dr. Seuss' properties, and location of The Dr. Seuss website.  You can look at their page of suggestions and resources for "Read Across America here, and get some printable certificates here.

KidThing: Have a free donloadable animated book of Horton Hears A Who

Math Stories
http://www.mathstories.com/bookstories/Book_12_Dr_Seuss.htm
 
Oobleck Science
http://www.teachingheart.net/bartholo.html
 
Seuss graphics
http://www.afn.org/~afn15301/seussfiles/seusspics.html
 
Seuss Links
http://www.teachingheart.net/drsuesslessonlinks.html
 
Oh, The Places You’ll Go (grades 5-6)
http://www.teachingheart.net/ohtheplaces.html
 
One Fish Two Fish red Fish Blue Fish
http://www.teachingheart.net/onefishtwo.html
 
Interactive Seuss Fun
http://www.teachingheart.net/interactsuess.html
 
Cat in the Hat Ideas
http://www.teachingheart.net/catinthehat.html
 
Seuss Activity Sheets
http://www.teachingheart.net/drsuessactivity.html
 
Hurray for Diffendoofer Day
http://www.teachingheart.net/hooraydday.html
 
Read Across America Project
http://teach.fcps.net/trt4/Dr.Seuss.htm
 
Read Across America Linkshttp://www.usd267.com/TL%20Student%20Pages/readacrossamerica.html