This is a pretty good site for trailers. The Avengers trailer is from Comicon. Mainly the logo. Narrated by Nick Fury:
Movie-List - The Avengers (2012) Trailer Page
This is not the same exact trailer as previously seen Helmets abound:
Movie-List - Thor Trailer Page
Movie-List - The Avengers (2012) Trailer Page
This is not the same exact trailer as previously seen Helmets abound:
Movie-List - Thor Trailer Page