The sites I use most are these:-
For machine translation, there is of course Google Translate but a better option most of the time is Span¡shD!ct which offers not only translation but a huge dictionary and also grammar and lessons should they be required. WordReference is a site with a dictionary that has a large number of example phrases showing how words are used.
To practice speaking and listening, I joined italki which offers both professional teachers and also facilitates finding language exchange partners. It is through this site that I have made a number of Spanish friends. I have also recently joined Verbling where you can join classes with several people at the same time