I don't know if there is a list - but you can browse both their instant and mailing selections without signing up for an account.
I can tell you as a netflix subscriber that they now have some really great stuff on there. They signed a deal with Starz to get what appears to be any movie that is was/is on Starz which includes a lot of new and older movies.
They have a deal with NBC and CBS too I think - you can get Heroes season 3 episodes on Netflix on the Tuesday after they air on Monday - which means you don't have to go to Hulu or the NBC site and sit through commercials - you can even put those upcoming episodes in your que so they'll play automatically for you.
They just seem to be adding more and more and more to their streaming section every day - so far I love it.
Maybe I'm blind, but is it possible to see a full listing of Netflix titles that are streamable online without signing up? I'm considering getting a Netflix subscription and Roku box for my wife for Christmas, but I know she would use it primarily for streaming. I see that that there is a "smaller library" of streamable content, but I can't seem to find a full listing. Just trying to get an idea of what's NOT available, really. TIA.