Safety Data Sheets (formerly Material Safety Data Sheets): SDS on the Internet

The most effective Google search for SDS is using:

"Safety Data Sheet" +substance
[use quotation marks as shown above] 

For example, "Safety Data Sheet" +aspirin

Using the plural "sheets" will pull up more results, but they will be covering theory and will not contain the actual data sheet. 

Individual sheets also tend to not have the acroynm SDS on the title page. 

Google will also find occurrences of the substance in the body of an SDS, not just in the title - especially if it is a component of another compound - e.g., "aterial Safety Data Sheet" +benzene will pull up  an MSDS for 3,3'{1-[(Phenylamino)Carbonyl]-3,4-Tetrazolium}-Bis(4-Methoxy-6-Nitro)Benzene Sulfonic Acid. 

There are a number of companies attempting to make money by selling copies of individual SDS, so a Google search may pull up a link to a listing of MDS that are available for purchase without showing the actual text.  Using Advanced Search in Google, you can limit your search by document type - you may wish to try limiting your search to just PDF document types in order to get full-text instead of a purchase option.

• MSDS Hyper Glossary.  Definitions of terms used in MSDS
• How to write a Material Safety Data Sheet 
  A beginning guide to writing your own MSDS if it doesn't already exist elsewhere.
• SDS FAQ     
  Gives an excellent history of SDS and basic information about them.
• Using Materials Safety Data Sheets.  By Anne Marie Helmenstine, Ph.D., About.com Chemistry guide. All about what SDS contain and how to use them.