Readers who have poked around my book recommendations would know that I think Huehnergard’s A Grammar of Akkadian (3rd ed.; with its companion answer key, Key to a Grammar of Akkadian) is the best around. The Ancient World Online blog notes that the vocabulary for this grammar is available in online flashcards. Pretty cool.
Believers in Zecharia Sitchin’s “work” in Mesopotamian texts can ignore this.