Online Workshops offer some general information about conditional sentences:

http://www.kle.nw.schule.de/gymgoch/faecher/englisch/material/worksheet/if.htm

http://www.dockingbay.de/topen.html?http://www.dockingbay.de/engl/open.html

http://www.english-zone.com/grammar/if-thenpres.html

http://www.edufind.com/english/grammar/IF8.cfm

http://kfmaas.de/gram_if.html

Excercises on if-clauses:

http://www.iei.uiuc.edu/web.pages/grammarsafari/journal_condit.html

http://www.lothar-kissinger.de/grammar/if.htm

http://iteslj.org/quizzes/vm/if-clauses.html

http://www.english-zone.com/grammar/if-then3.html

http://www.english-zone.com/grammar/if-then5.html

http://www.better-english.com/grammar/if.htm