Por y para
http://legacy.lclark.edu/~benenati/porpara/porpara.html NOTES
http://www.bowdoin.edu/~eyepes/newgr/ats/43.htm NOTES on top, practice on the bottom
http://www.drlemon.com/Grammar/por-para.html NOTES
http://legacy.lclark.edu/~benenati/porpara/porpara1.html
http://legacy.lclark.edu/~benenati/porpara/porpara2.html
http://legacy.lclark.edu/~benenati/porpara/porpara3.html
http://legacy.lclark.edu/~benenati/porpara/porpara4.html
http://legacy.lclark.edu/~benenati/porpara/porpara5.html
http://www.studyspanish.com/practice/porpara.htm
http://www.spanishnewyork.com/automatic/porpara.php
http://www.spanishdict.com/topics/practice/10
https://personal.colby.edu/~bknelson/SLC/por_para1.php
https://personal.colby.edu/~bknelson/SLC/por_para2.php
http://www.trinity.edu/mstroud/grammar/porpara2.htm
http://www.conjuguemos.com/activity.php?language=spanish&id=28&source=public&
http://www.123teachme.com/spanish_sentence_quiz/category/por_vs_para_1
http://www.quia.com/quiz/112398.html
http://www.learnspanishfeelgood.com/prepositions-para-por1.html
http://www.learnspanishfeelgood.com/prepositions-para-por2.html
http://www.learnspanishfeelgood.com/prepositions-para-por3.html
http://www.learnspanishfeelgood.com/prepositions-para-por4.html
http://lrc.salemstate.edu/aske/webexercises/porpara01.htm
http://www.quia.com/ba/74048.html
http://www.spanish.cl/Grammar/Games/Por_Para.htm
http://wps.prenhall.com/wl_heining_anda_1/87/22459/5749619.cw/index.html