Langenscheidt e-Dictionary provides a very good source of information both for professionals and new learners. The dictionary covers over 245,000 translations for each language.
This is the most comprehensive Spanish-English dictionary and thesaurus with 600,000 translations and 4 million synonyms covering idiomatic, technical and general terms.
CONTEXT is bi-directional dictionary containing 10 language pairs: English to/from French, Italian, German, Portuguese, Serbian, Spanish and French to/from German and Italian.