Thalia,
I'm a native English speaker who studied and used Spanish, and I have a few suggestions.
1. Destinos
Destinos is a television course created by Annenberg Media, the same folks who produced French in Action and Fokus Deutsch. It is shown on public television in many cities, and can be found in many libraries, but there's a more convenient option: if you have a fast Internet connection, you can watch the shows for FREE from their website:
http://www.learner.org/
There are 52 half-hour lessons, set up as a "telenovela." The actors speak somewhat slowly (unlike French in Action, which is full-speed Parisian), and there is a lot of repetition, but the story is so interesting that I forgot I was watching in Spanish by the end.
2. Spanish audio magazines
There are a couple of magazines written for learners that come with transcripts and audio CDs. Puerta del Sol is a bimonthly from the Champs-Elysées group (they do French, German, and Italian, too):
http://www.champs-elysees.com/ The announcers and content are mostly from Spain, and it might be a little advanced. Think Spanish is a monthly with content from the whole Spanish-speaking world, and maybe more geared to your level:
http://www.readspanish.com/
Having interesting content with both audio and text is a great way to go.
3. Reading material
I agree with you about childrens' books--there is a limit to how much you can do. There are simplified editions of real texts, although not as many as for English. If you type "Spanish Easy Readers" in Amazon.com, you should see a number of books.
The other suggestion I have is to read books in Spanish that you've already read in English, or know the story from a movie. I could read The Godfather in Spanish fairly early on. There are so many Spanish translations of English books nowadays, including nonfiction on subjects of interest to you. You can then go on to original Spanish works, especially if they have a glossary. (Rosaura a las diez by Denevi was easy to follow.)
4. DVDs
I originally got a DVD player because I realized what a great language learning tool it was. Many DVDs come with a Spanish language track (French is more common because of the Quebec market). You can try it with English or Spanish subtitles, then without. Again, you can start with easy American films like Disney, then try an original Spanish-language movie like El Norte or El Mariachi.
5. TV
Most big cities have shows in Spanish, and the news is relatively easy to follow, since the language is straightforward, and the content familiar. If you can't get TV broadcasts, try the Internet.
www.mediahopper.com is a good resource.
6. Internet
Besides the Internet sources mentioned above, there are tons of sites in Spanish that also have English equivalents. The U.S. government and many commercial enterprises have websites in Spanish; you can flip to the English to see what they're about. Also try
www.about.com and find the Spanish Language page, which has a slew of material.
7. Living in the U.S.(!)
It's hard to go anywhere and NOT run into Spanish language material, usually with English equivalents. The government has brochures in both at most libraries, stores like Home Depot, Sears, and Best Buy have Spanish translations in many departments, and of course, there are native speakers all over the place.
It may be a little harder to get material for other languages than for English, but you can certainly use the Antimoon method for Spanish (and other languages) if you're resourceful.