I am always in search of the latest and greatest tools; however, sometimes it is helpful to revisit the tools that have been around for awhile.
One of my favorite tools is Blachan Shahi - a free visual dictionary.
You can easily use this tool in your classroom by having students enter in a vocabulary term of their choice. They will receive a text definition along with Flickr images.
This is a great way of scaffolding learning for students. They are able to read the text definition of the term, as well as have a visual to solidify its meaning.