Here is a list of ideas for the theme of your forum.

• graphic/design
  
• coding/programming
  
• website developement
  
• advertising
  
• games (card games, board games, etc.)
  
• forum games
  
• video games
  
• music
  
• videos
  
• classical stuff
  
• jobs
  
• school/college
  
• groups
  
• places/cities
  
• food
  
• computer support
  
• computer developement
  
• computer games
  
• website games
  
• console support
  
• general forum
  
• debates
  
• religions
  
• regions
  
• relationship support
  
• education/learning
  
• technology/creations
  
• website support
  
• fan groups
  
• support (in general)
  
• friends
  
• parties
  
• fashion
  
• ideas
  
• sports
  
• activities
  
• culture
  
• languages
  
• current events
  
• jokes
  
• riddles
  
• short stories
  
• poems
  
• television shows
  
• weather disasters
  
• disasters
  
• raising a family
  
• super stitions
  
• ghost stories
  

I hope these help