I am tired ov everyone saying 'searchbar' in every thread, but it is almost always negligence on the part of the OP, so I came up with an idea.
You enter your title, and a tiny box pops up, kinda like setting your password for gmail or something. If the potential poster's thread title matches any other, the OP should be kindly reminded to search the topic.
Lets use a hypothetical topic 'Global Warming'
-The OP enters their thread title, and there could be a handy button you could press, and it determines if the same thread topic has been used before.
ex: OP types in 'Global warming', then presses the magic button and results are given
(this is assuming common words are automatically omitted from the search.
-The title box updates itself with every word typed, and it could use cool color combinations with each level of threat.
ex: OP wants to type 'Thoughts on global warming?'
'thoughts on' could yield a green/good to go indicator, then it would turn orange once 'global' has been typed, then 'warming' will prompt the user to search the topic (or it could provide a link which brings you the results of the 'global warming' topic.
I know that was confusing and possibly impossible to implement, but I thought that I'd share my idea.