John Minsheu produced a Spanish-English dictionary in the late 16thC, revised and re-published in the early 17th. King's College, London has a searchable facsimile online as part of their Early Modern Spain site.
Since it's come up in conversation a few times recently, I thought I'd add it to the website.
Early dictionaries can be really useful when you're trying to understand renaissance texts, especially when we're trying to translate technical, jargon-terms that may have fallen out of use in the modern version of a language. In addition, they're often great fun. John Florio's Italian-English dictionary is especially colourful.