NexusDB

SQL92:
http://www.contrib.andrew.cmu.edu/~shadow/sql/sql1992.txt (last full standard draft before approved; ~1.7megs)
http://www.contrib.andrew.cmu.edu/~shadow/sql/sql2bnf.aug92.txt (bnf)
http://developer.mimer.se/validator/parser92/index.tml (conformity checker)
http://csf.colorado.edu/local/sql/

SQL99:
http://www.ncb.ernet.in/education/modules/dbms/sql99index.html (last full standard draft before approved)
http://developer.mimer.se/validator/parser99/index.tml (conformity checker)

SQL2003:
http://www.wiscorp.com/sql/sql_2003_standard.zip (last full standard draft before approved; careful: ~10megs!)
http://developer.mimer.se/validator/parser200x/index.tml (conformity checker)

General:
http://www.wiscorp.com/SQLStandard.html
http://members.tripod.com/er4ebus/sql/ch01.htm (Teach Yourself SQL in 21 Days)