What Forum Software should I use?
Either php/mysql or aspx/sql
I checked out a similar thread but there weren't any real answers...
By far I would say PhpBB3, it has a bunch of user generated themes and addons, as well as an active development team working on enhancements and security updates. It is very simple to install and very robust in features. As the name implies, runs with PHP and uses MySQL (as well as a few others).
This is very subjective. Different people have different tastes hence varying favorites. For me, it is Vanilla Forums.
We use PHPBB3 on Windows servers, that works great as well.
I can recommend against bbPress, on the basis of its glacial development cycle and small developer community for addons (many have abandoned bbPress, notably ck who produced a good deal of important extensions but is not updating them for v1.x). Even though it's related to WordPress, it does not integrate easily with WordPress.
I recommend phpBB for the same reasons given by other writers. For free software, it's very good. (If you want commercial, I'd look at Invision Power Boards or xenforo.)