Woltlab BB (1.2) is free, simple and powerful. For a php-illiterate setting it up running takes 30 minutes. I've had Woltlab for nearly 2 years, and never had any problems with it - other than my dumbness maybe.
Most phpBBs look the same. Seeo ne of them, have seen all of them. The subsilver standard skin scares me away very fast. You have all seen Inviosions and phpBBs all way around, so maybe some examples of Woltlab then..
http://www.woltlab.de/en/forum/index.php?sid= (woltlab's site. you will find the download of the wBB in the first page somewhere, just choose the english version, not german)
http://wbbhost4u.com/wbb2/index.php?sid= (a forum mod/ host example)
http://www.bodynet.org/forum/main.php (a bodybuilder place, in italian structure)
http://www.anorexia.wbbhost4u.com/forum/main.php (eating disorders and other, multilingual)
http://www.bsolinks.com/wbb2/index.php?sid= (just a really nice skin there)
So, those examples just to show some ways it's been used .. to fit different styles.
The only thing I'd rally consider changing to from woltlab would be vBulletin - and that if there were 20,000 + people active on the boards.
