Besides Daniweb, there are many others, but it would help to have more specific information. For example, exactly what kind of technology are you interested in? There are forums for Apple users, Android users, Nikon users, programming in Python, etc.--just about anything.
You could do a generic search on Google for large forums, but you'd be better off being more specific. For example, use Google's Advanced Search capabilities to find a forums specifically about the topic of interest. Most forums have the word "forum" in their URL, so when I am looking for a forum, I usually ask for that term to be in the URL:
inurl:forum android forum
Try to narrow it down as much as possible or you'll spend a lot of time going through lists of irrelevant forums.