vBulletin

Industry leading software and support

I have only had positive experiences with vBulletin, It is easy to use and very customizable. The admin control panel provides numerous settings to fine tune how your community works and looks.
On serveral occassions I decided on another forum software when starting a new community, but I always keep gravitating back to vBulletin Due to it's widespread use, it is very easy to find a theme or an addon for your community, as there are many out there. There also exists a semi-official modification site hosting thousands of styles and modifications, it can be found at www.vbulletin.org.
Highly recomended.