A very good tool for looking up definitions because it provides great examples of them. Also it is very useful for finding phrases and terms like that because there is a blog in which people can add their own comments and suggestions about a term or translation.
Del portal de la Real Academia Española se puede acceder a diccionarios, gramáticas, corpora, bases de datos, obras académicas, literarias y lingüísticas en lengua española.
V. Ambati, S. Vogel, and J. Carbonell. Proceedings of the ACM 2012 conference on Computer Supported Cooperative Work, page 1191--1194. New York, NY, USA, ACM, (2012)