I don't know of any other good off-topic forums. I do know of one extemely long running off-topic thread though.

Over at www.digitalspy.co.uk (a site that covers UK digital television) there is a thread in their "Digital satellite" forum that has been running since 3rd March 2002 and covers 217 pages at the latest count.

http://forum.digitalspy.co.uk/board/t/19146/ds.html

The thread is titled "Interactive F1-The Verdict" and started off talking about the Sky F1+ Interactive Formula One Grand Prix service, which itself ceased to exist last October anyway...