I need some idea's as to what you would want on a movie blog and forum. Blog will be running Wordpress and I forum in a month will be running vBulletin. But for now it will be running with either MyBB or phpBB.
To be honest, If you're looking to run a blog, you should do it on something you love or are good at. If your asking for ideas it must not be one of your favourite interests. But basically you could add movie reviews every day to the blog. And different types of movie cateogires to the forum giving the chance for members to discuss new/old and upcoming movies.
Movie reviews, gossip, movie trivia and a lot more things like that would help. In forums, you could make it the way IMDB is.. forum for discussing upcoming or new movies and so on.
The first question you should be asking yourself is: Are you planning to run a legal content site or illegal content site. If in case you are going to post movie download links and etc, then having a blog & forum contradicting each other would be a big joke. The second question you need to look at is : Do you have the time and management skills to run 2 completely new sites ? Most of the forums fail due to one of these 2 reasons. Individual sites/blogs are quite different from forums. Ultimately decisions rests up on you to make up your mind for us to give you a proper valid suggestion.