ONLINE RESOURCES
TAFSIR
Compare selected English Translations of Quran: https://quran.com/
Tafsir al-Jalalayn, a brief and simple classical tafsir: http://shamela.ws/browse.php/book-12876/
Sabuni's Safwat al-Tafasir, a relatively easy contemporary tafsir: http://shamela.ws/browse.php/book-8967
Collection of 7 Arabic tafsirs, including Ibn Kathir: http://quran.ksu.edu.sa/tafseer/
Collection of MANY Arabic tafsirs: http://Furqan.co/
GRAMMAR
Word-by-Word grammatical, morphological and meaning analysis (in English) for the Quran: http://corpus.quran.com/wordbyword.jsp?chapter=1&verse=1
Simple I`rab al-Quran: http://quran.ksu.edu.sa/tafseer/eerab/sura1-aya1.html
DICTIONARIES AND LEXICONS
Al-Maany Arb-Eng dictionary
Ejtaal Arabic Almanac, includes online Hans-Wehr (Arb-Eng) dictionary, Lane's Lexicon (Classical Arabic to English), Lisan al-`Arab (Arb-Arb) and others, all in searchable PDF format: http://ejtaal.net/aa/
Search for all Quranic occurrences of a particular 3-letter root: http://corpus.quran.com/qurandictionary.jsp?q=smw
Baheth Arabic lexicon search engine, searches 5 classical dictionaries, including al-Qamus al-Muhit (a nice, brief, classical lexicon) and Maqayis al-Lugha (which tries to identify the underlying meaning(s) of each root): http://baheth.info/