philolog.us - There is a great, comprehensive Latin dictionary under the ‘Lewis and Short’ tab. It has information on meanings, irregular forms, usage, etymology and examples taken from Latin authors that show how a given word is used in context
Wiktionary, the free dictionary - Wiktionary can be pretty helpful as a simpler dictionary. It is possible to search any form of a word, which helps out if you have issues identifying something. It’ll usually provide meanings, conjugations, and occasionally etymology and related words. It isn’t as in depth as phililog.us, and I have had moments where the information listed on wiktionary has been wrong, so double check with other sources if you can
Latin-English- This dictionary can be useful for giving multiple meanings and forms which are possible for a given word. This dictionary is particularly useful when identifying words and their forms while translating. There are places where there can be incorrect information listed, so try to double check with other sources.
Perseus Digital Library - This site has a large library of Latin texts. It can also show you the breakdown of a given word’s grammar, but I have found that it isn’t always totally accurate.
http://dcc.dickinson.edu/vergil-aeneid/vergil-aeneid-i-1-11 - This is a good commentary for Vergil’s Aeneid that seems to be aimed at beginners, with lots of vocabulary and grammar notes. Also includes selections from the text itself.
http://vergil.classics.upenn.edu/vergil/index.php/ - This is another site on the Aeneid that combines a couple historical commentaries and translations with a grammatical analysis of each word, including its case, number, gender, tense etc. with its syntax (i.e x is a direct object of y, a modifies b)
ET Merrill, Commentary on Catullus, Poem 1, line 1-3 - This is a commentary on the poems of Catullus, organized by poem and line number. While it seems aimed at more advanced students of Latin, it does include all the poems.