While not an exhaustive list, I find these tools to have endless possibilities to promote independent, authentic language learning in an ESL classroom:
Voicethread is a very user-friendly communication tool that allows students to practice listening and speaking skills using photographs and even video.
Tokbox allows students to interact by instant message and video chat. It provides endless opportunites for students to interact with people both within and outside of the classroom.
A great resource to both listen to authentic input as well as for both students and teachers to create their own podcasts!
A tool that promotes student collaberation,and negotiation of meaning, and gives students something to show for it.
Twitter can connect classmates and allow them to produce language in managable chunks. For teachers, if you can find the right tweeters, it provides a wealth of resources for your classroom!
http://vocabahead.com/Home/tabid/37/Default.aspx
Vocabulary words are defined in context. Students can create their personal vocabulary lists, and collaberate with classmates to create lists and tests.
A wealth of authentic language input, YouTube also allows students to upload their own videos.
Email is an important communication tool, and I believe gmail is one of the best. Additionally, igoogle gives access to instant messaging, creating and sharing documents, search engines, site building, interactive maps- a CALL treasure!
User friendly, students can create a website with a built in blog for reflections among other uses.
A great place for teachers to keep track of online resources and tools, students could also use it to store and share links.