The MYWordBook app is a product of the British Council and Cambridge University Press. The app functions as a vocabulary notebook, allowing you to input words, translations, pictures, notes, definitions and example sentences. The app is available for use with Iphone, iPad, Android, and Blackberry. While the app is free, you must pay for the word packs that come with it. A problem with these word sets is that they don't seem to be in any order of frequency or word list. There is the option to create your own word list however.
This is my favorite online dictionary for L2 purposes. It contains several translation dictionaries between English and Spanish, Chinese, Arabic, and several other languages. It also has conjugation charts (when you look up words), translations for phrases, and forums. The website also has plenty of examples.
I have used this website for years when working in Spanish, and I have found the forums particularly useful when trying to translate something tricky. Also, when searching for a multi-word phrase, I recommend using quotation marks.