Not forums where you post and network, but news and info sites where you keep up on the industry.
Mine are:
http://boxofficemojo.com/ (I'm a box office stats geek)
http://beta.rottentomatoes.com/ (although they JUST redid their web site and I hate it now because something has gone screwy with the navigation)
http://www.aintitcool.com/ (but I admit they're not exclusively film)
http://imdb.com/
And if I had the money, I'd subscribe to Variety.
Oh, and I also frequently use
http://www.fandango.com/
for merely CHECKING on movie times (but rarely for actually buying the tickets).
Mine are:
http://boxofficemojo.com/ (I'm a box office stats geek)
http://beta.rottentomatoes.com/ (although they JUST redid their web site and I hate it now because something has gone screwy with the navigation)
http://www.aintitcool.com/ (but I admit they're not exclusively film)
http://imdb.com/
And if I had the money, I'd subscribe to Variety.
Oh, and I also frequently use
http://www.fandango.com/
for merely CHECKING on movie times (but rarely for actually buying the tickets).