Briefs Nationwide!

Reviewing the parties' briefs is a useful way of gaining addition insight into a judicial opinion. However unlike the opinions briefs are not uniformly published or indexed. 

While finding briefs is more difficult than opinions it is possible. The Yale Law Library has put together a excellent guide to finding state court briefs here:

http://library.law.yale.edu/state-court-records-and-briefs

The United States Supreme court has a page detailing where to find briefs before that court here:

http://www.supremecourt.gov/oral_arguments/briefsource.aspx

The ABA maintains a fairly good collection of SCOTUS briefs from 2007. However the SCOTUSblog page has the best web interface to find SCOTUS related filings. 

Unfortunately federal appellate briefs are only available through PACER. You can sign up for a paid PACER account to receive 15$ of free usage per quarter. You can then make use of the PACER document sharing collective RECAP. 

Oregon appellate briefs are available for cases since 2007 through the State of Oregon Law Library here:

http://digitallawlibrary.oregon.gov/