I have been an English tutor for several years. (I am moving to a major university and am looking to do the same there.) Anyway, the English professors as well as my boss swear by Fraklin electonic dictionaries. They there own Web site as well as an 800 number. They will be glad to send you a free catalog too.
Here's the link to their site:
http://www.franklin.com/
I do not know if they have unabridged dictionary, but you can look through the site or call their 800 number. It is 1-800-266-5626. Most of the students that I have worked with have only been speaking English for a few years and they had Spanish/English electornic dictionaries.
God luck ya'll. Let me know what you found out.