Over on the Internet Evangelism Day pages at gospelcom website is a list of 52 questions to help assess your church website, looking to improve its use as an outreach tool.
I am not totally convinced by the scoring system they use, but at least there is some (limited) information about why each question might be relevant.
I particularly like number 25;
Within the norms of your culture, does the writing style of the website demonstrate informality and self-deprecating humour?
This is a (long) thought provoking list which is worth looking at, but it is not definitive. It could have linked to more information on each point, for instance on the subject of web accessibility.
Found via: Church central