It looks like a much better Spanish-English dictionary is available now, as May 26, 2011. ($16.99)
http://www.amazon.com/HarperCollins-...dp/B0052ZQNVI/
Claims to have 255,000 entries versus the 50,000 entries in Barron's, which was the previous best (I think).
It is formatted so that it can be the default Kindle dictionary.
I still did not find a decent all-Spanish Kindle dictionary (Spanish to Spanish). I am wondering, when someone buys a Kindle in Spain or Latin America, does the Kindle come with a Spanish dictionary at all?