Intermediate Grammar Links
Simple past
http://owl.english.purdue.edu/handouts/grammar/g_tenses2.html
Progressive
http://www.longman-elt.com/ae/azar/FCtoc_UUEG.htm
Simple present
http://www.longman-elt.com/ae/azar/FCtoc_UUEG.htm
Future
http://www.longman-elt.com/ae/azar/FCtoc_UUEG.htm
Subject/verb agreement
http://grammar.ccc.commnet.edu/grammar/cgi-shl/quiz.pl/sv_agr_quiz.htm
http://grammar.ccc.commnet.edu/grammar/cgi-shl/quiz.pl/agreement_add2.htm
There are several quizzes on the same topic in this site
Modals
http://www.longman-elt.com/ae/azar/FCtoc_UUEG.htm
Passives
http://en.wikipedia.org/wiki/English_passive_voice
http://owl.english.purdue.edu/handouts/grammar/g_actpass.html
http://grammar.ccc.commnet.edu/grammar/passive.htm
http://www.smccd.net/accounts/sevas/esl/reviewlesson/passivesum.html
http://owl.english.purdue.edu/handouts/grammar/g_tenses2.html
http://owl.english.purdue.edu/handouts/print/grammar/g_passive.html
Grammar quizzes
http://grammar.ccc.commnet.edu/grammar/quiz_list.htm
Azar workbook
http://www.longman-elt.com/ae/azar/FCtoc_UUEG.htm
Grammar links
http://www.aitech.ac.jp/~iteslj/quizzes/grammar.html
http://www.edufind.com/english/grammar/toc.cfm
http://www.edunet.com
http://www.english-zone.com/grammar/
http://www.iei.uiuc.edu/web.pages/grammarsafari.htm
http://www.iei.uiuc.edu/structure/structure1/salzmann_index.html
http://www.iei.uiuc.edu/web.pagesgrammarsafari/.html
http://www.manythings.org/voa/
Humorous grammar rules
http://www.creativeteachingsite.com/humorgrammar.htm
Grammar exchange
http://www.longman.com/ae/azar/grammar_ex/index.html