One of my favorite plugins to use when building communities with WordPress is bbpress. Besides being light wieght and easy to configured it is pretty robust in what it can handle. I have built some huge communities and as long as the server isn't made out of butter it does pretty well.
But the one thing that really drives me crazy is the look. Bbpress has not change the look of the forums since they release it I believe. I guess that's ok if you don't mind your forums looking outdated.
The Good News
Over the years I have made so many forums with bbpress I save a base style sheet that I use from the start and go from there so I am going to share one of them with you to use as you see fit. For the most part it is nothing really drastic just something I use to get started with before I do any serious customizations. (note that these styles will not style any fancy bbpress third party plugins you may use just the default bbpress plugin).
These style are done with LESS variables for quick editing. I would recommend you use custom less plugin or with Custom CSS plugin from Jetpack. If you go the Jetpack way be sure to turn on the LESS preprocessor to the right.
***I may update this post from time with a couple more.***
***Note that these work best if you are starting a new bbpress forum.***
Thanks for reading and I hope you find some value here. If you have any question post them in the comments.