I think Mariek's advice is excellent. You'll need Gildersleeve's grammar if you want to know Latin inside-and-out, and it will be clear why once you've consulted it a few times: it is the most comprehensive Latin reference available in English (to my knowledge). From personal experience and from the advice of people who know Latin far better than I do, if you want to learn Latin seriously you must buy this book.<br /><br />It is certainly possible to learn out of a grammar, I learned most of what I know about tenses and moods by carefully copying the important bits out of Gildersleeve. Charts can be constructed and memorized (if I see an independent subjunctive, there are x, y, and z possibilities for what construction it is). Be warned: there are many grammatical exceptions and Gildersleeve won't hold your hand, to his infinite merit. <br /><br />You'll need more. Extensive reading is a must, and that means authentic Latin texts that are well-annotated regarding grammar and style, most likely written for Victorian schoolboys. Skip Latin readers, which are by definition fake/simplified Latin, except when you need light reading (which might be often if you read real Latin with intensity and commitment). Choose to read works that appeal to you. Do you like war? Have an historical interest in Latin? Read Caesar or Livy. Cicero is a must and you might take a look at the offerings here at textkit.<br /><br />On breaks you might be entertained by reading early humanist treatises on education (in Latin of course). There can be some found in PDF form at the bibliotheque national: http://gallica.bnf.fr/scripts/Consultat ... &O=N064979
"De Formando Studio" by Rudolf Agricola, Erasmus, and Melanchthon. You'll feel inadequate when you learn about the rigor with which people like John Milton, or Michel de Montaigne (speaking fluent Latin by 6!) prosecuted their studies.<br /><br />Just keep reading, do whatever it takes to stay motivated. Fill up notebooks with Latin quotes, memorize passages, make careful notations about the difficulties you have.<br /><br />I'm still curious as to why you'd like consummate knowledge of Latin. There are many languages one can attain consummate knowledge of, but why choose Latin? Why not a modern language? Or for dead languages, Greek? Or Akkadian for that matter? What is it that drives you about Latin?