Willing to pay the price for one of the best ones? vBulletin
Want vBulletin-equivalent(except for some features) for free, with addons that are easy to add? MyBB, or SMF.
Want a super-simple, plain, less resource hungry? Vanilla
I never recommend phpBB because its a PITA when it comes to managing things like installation/uninstallation of addons. Moreover, it has worst reputation for security standards. On the other hand, MyBB and SMF are beating most of the other forum packages. phpBB is also not as scalable as other well-known forum packages. You board will crawl when it gets huge!