This is a list composed during the USC Differentiated Curriculum training I went to presented on Integrating Technology into Language Arts by Julia Nyberg. Some of these are favorites; others were new to me. I believe all are free.
www.mindmeister.com - mind mapping software
www.eduglogster.com - create a poster with video, audio, and art.
www.voicethread.com - video sharing and collaboration
www.makebeliefscomix.com - drag a setting and characters into a comic strip that students can then narrate
www.wordle.net - creates word clouds using text you provide
www.readingrockets.org - video archive interviews with some famous authors
www.teacher.scholastic.com/activities/swyar - reviews of books by students
www.speakaboos.com - read aloud books to students
www.storybird.com - students can create online books
www.polleverwhere.com - can create a simple online poll. Students can text their answer using mobile devices.