I've learned French and Italian, and I must have tried half the books and CD sets available on the market.
I agree with the others who found Rosetta Stone overrated. While it's a great way to learn basic vocabulary, there's no grammar instruction and you don't learn anything about the structure of the language.
If you're looking for a refresher in German I would recommend the Pimsleur CDs. Somebody says (in english) "I walked to the store today", there's a pause, and then they'll repeat the phrase in German. They work their way up from basic sentences to more complicated ones, and slowly add new words. There are 30 half hour lessons per CD set. I think this would be a good way to remember the stuff you've forgotten.
If you want to learn Spanish from scratch then I would recommend one book that covers grammar, one book that covers verb conjugation (with lots of exercises), and the Pimsleur (or any similar) audio series for practice.
Another good learning tool is flash cards. I've bought a couple sets of flash cards from
http://www.flashcardco.com/ that were great in helping me build a solid base vocabulary.
I think most of it comes down to how you learn, and what you're looking for out of the language. I'm analytical and don't mind learning things by rote, so of my recommendations are based on what worked for me.
Anyways, all that said, no book or CD set can give you "real conversation" practice that's essential to learning a language. I spent only 4 months in Italy, and my Italian improved more than it did during the previous 8 months of fairly intense studying. I'm sure you're busy, but if you could manage to meet a Spanish speaking person once a week for lunch to chat in Spanish I think it would be more valuable than any learning material you could buy.
Good luck!