VoiceThread 4 Education by has a rich collection of voicethreads at every grade level. A great resource for getting ideas.
A Collection of Voicethreads on PageFlakes - elementary level
MathCasts - a collection of how-to math videos aligned to national standards. MathCasts collection search on Voicethread.
Ms. Ngai's 2nd Grade classroom - Great examples of how voicethread can be used in the primary classroom.

VoiceThread's Digital Library (small but growing collection of examples of how VoiceThread is being used in the classroom)