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Sifre (on Bamidbar and Devarim) https://he.wikisource.org/wiki/%D7%A1%D7%A4%D7%A8%D7%99 Netziv - assuming you mean HaEmek Davar (and not Davar HaEmek or one of the others), Sefaria has most of it: http://www.sefaria.org/Haamek_Davar_on_Genesis http://www.sefaria.org/Haamek_Davar_on_Exodus http://www.sefaria.org/Haamek_Davar_on_Leviticus Bamidbar will be ...
Hebrew: Ibn Tibon, Schwartz, and Kapach: http://mobile.tora.ws/ Schwartz: http://press.tau.ac.il/perplexed/toc.asp Kapach: http://www.daat.ac.il/daat/mahshevt/more/shaar-2.htm English (Friedlander) http://www.sacred-texts.com/jud/gfp/ If you're looking to pick a single one for Hebrew I would personally go with Kapach, but that's completely personal ...
It's not a Jewish site, but you might find exactly what you are looking for at http://www.e-sword.net/. You download it, and when you open it up you'll find a bunch of English translations. It's a very powerful program, with all sorts of cross reference features...not bad for free!
In addition to the links provided in J.C. Salomon's answer, there is an HTML page with a very readable typed and color coded version of ויכוח רבנו יחיאל מפריס on the Daat website here.
HebrewBooks.org has the 1873 Thorn printing of ויכוח רבנו יחיאל מפריס Vikuach Rabeinu Yechiel meParis (alternate scan), and the 1928 Lwów (= Lvov = Lemberg) printing, ויכוח רבנו יחיאל מפאריז (alternate scan).
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