Flashcards! (Tarjetas)

Anki.  Flashcards are a great way to learn and study a language! 

Brainscape. If you want to create flashcards online, this is a great resource.

Studyblue.com. Here's another great Flashcard engine online. 

Quizlet.com. Create flashcards and quizzes to help study your Spanish vocabulary here too!