You always seem to reference traditional cardboard flashcards, but have you checked out some of the more powerful electronic flashcard tools? You can set them up any which way you want them to. From quizzing sentences to fill-in-the-gap type exercises. They also give you the ability to add multimedia to the text, some of them even have thousands of words prerecorded. I was planning on feeding my application with voice samples from SpanishPod to help with pronunciation and example sentences to get context.

Anyhoo. I learned English as a second language in High School. In the 10th grade we started using a "Learner's dictionary" that was monolingual, much like the example anna8 posted about the Spanish/Spanish diccionario. Wow, how I wished we could have used that sooner. It makes so much more sense. Mind you, it's very frustrating at first. Sometimes you had to look up two additional words to find out what the word meant, you were looking up in the first place. But you get used to picking up words like that on the fly. And that's a great way to learn new words. So I definitely recommend getting a Spanish/Spanish dictionary.

And the flashcards are fine, not as a memory tool (unless you made them yourself and carefully wrote down the word-phrase-whatever then that exercise was good.) but as a self adminstered randomized test.  Go elsewhere and find meaning and internalize it.  Donperigo noted that simply and repetitively looking up and filling in blanks, doesn't cut it either. In one eye, out of the fingers and gone. You have to take time and be sure you OWN those words. You don't want to memorize the test, you want to understand the material.

Mi español-inglés diccionario se está deshaciendo y creo que estoy listo de graduarme á un diccionario todo en español (ojalá).

Tambien, he apprendido la palabra 'sugerencia' que me gusta mucho ;)

Que quiero decir:

I just ordered Diccionario Educativo Juvenil from Amazon too!

My Spanish-English dictionary is falling apart and I believe I am ready to graduate to an all Spanish dictionary (hopefully).

Also, I have learned the word 'suggestion' which I like a lot ;)

English may be the common non spanish interface here but L1  varies from German to Tagalong and on all sides and in between.

Spanish Stories / Cuentos Españoles (A Dual-Language Book)

Stories from Mexico : Historias de Mexico

Stories from Latin America : Historias de Latinoamerica

Éstos han ayudado aumentar mi vocabulario mucho. 

Para mi es mucho, mucho más fácile entender español escrito que español hablado.

Mi objectivo último, sin embargo, es hablar con otros.

How to Learn Any Language - Barry Farber. He speaks many languages and uses flashcards as part of his efforts for aquiring language.

http://www.alljapaneseallthetime.com/blog/10000-sentences-how - describes his use of flashcards as part of his study program. He taught himself Japanese in 18 months without taking any classes, while living in Utah and studying Computer Science in university.

http://www.victoria.ac.nz/lals/staff/paul-nation/Publications/2003%20Effective%20ways.pdf - Paul Nation is a researcher in Second Language Aquisition. Refer to his book (Nation, I.S.P., 2001, Learning Vocabulary in Another Language) for more information.

- learn in the direction English to Spanish, i.e., look at the English word or phrase and try to translate it into Spanish. (It's a good idea to start with the direction Spanish to English because it's easier, but that's not enough! If you don't learn from English to Spanish, you are wasting your time.)

- review your flash cards as often as possible; the first review is just as important as the 10th or 20th or 50th review. Review difficult cards more often than easy ones. (If you don't review the cards until you "own" the words or phrases, you are wasting your time.)

- find a comfortable way to learn with flash cards. (In the long run, it's all about motivation. If you don't like doing it, you will stop doing it. And then again: if you don't review the cards sufficiently often, you have wasted your time. My favourite way of learning flash cards is at home in an arm chair with a hot cup of tea using the "iFlash touch" app on my iPod while listening to music. :)

- use different cards at different levels of your learning process: in particular as a beginner you should learn phrases. Once you know several phrases and/or how to build new sentences, you might want to learn more words that you can use as building blocks. (If you just learn single words without a clue how to form sentences, you are wasting your time.)

- And, of course, vary the process and try other learning techniques in order to find out what works best for your. 

I guess I agree with JP that it is really easy to waste your time with flash cards; and maybe a lot of users of flash cards are actually wasting their time. However, I'm also convinced that it is possible to use them efficiently.