There are many masonic forums all over the net, but only few can be considered "serious". One of the most interesting ones is Mastermason.com's forum - featuring discussions on various topics. There is literarily something for everyone - for non-masons who are interested in joining, for newly initiated brethren, tyled forums for discussions that need to stay private :), it even has a "hobbies&special interests" section. It's administrated regularly, so there are no unnecessary or offensive comments.
A topic that caught my eye was "Travelling Men" - intended for introducing and accomodating visiting brethren. So - if you plan to travel - make sure you check it out!