Sorry - I'm going to have to come down squarely on the side of "Forums" here. When we use the word while speaking English, it is no longer a Latin word. It is an English word, so English convention should preside. Useage is the determining factor here. How do folks use it? Overwhelmingly, they use "Forums". It's "Forums"

All of the arguments I've seen here referencing Latin useage and historical useage pale. I'm not saying they're invalid, just inconsequetial.

So I'll know what folks mean if they bring up "Fora", but their tweed will be showing.