i've never been a member of a christian forum. just do a google search, lurk on a few to see what's up and if that forum does not confilict with your beliefs and then join if you want to.
You can also check MSN...for groups...search what every you are looking for...ie,...I search Apostolic groups. If you are into music...I like learngospelmusic.com. They talk about music, but about othe topics also.