In this answer, I am attempting to suggest what the logo and site design should be. I am combining the already existing (and up-voted) suggestions into this one answer. I intend to attempt to make this answer a full suggestion of what this site might look like entirely (every aspect of it). If you like it please up-vote, if you think something needs adding then please either give a comment or (if you can) edit it.
The Logo
I believe the logo should be the name Allah:
I pick this for a few reasons, one believing in Allah is the base of faith and Islam, every Muslim, no matter their sect must believe in Allah, this is one of the things all so called sects of Islam have in common (and to take it further, the believe in Allah/God is what all three Abrahamic faiths believe in). Secondly, Fahad Uddin, in His answer, mentioned that calligraphy is popular in Islam, so the above suggested logo/picture is a mild, easy to read (Insha'Allah) calligraphy form of the word Allah.
I think the logo should be in the middle of the site's header, with the following text (which I think should be a bit smaller than the width of the logo) under it:
Islam الاسلام
The Tabs
What I mean by tabs is the Questions, Tags, Users, Badges, Unanswered, and Ask Question tabs. I think, since the tabs are six all together, I think they should be split into three. So what I mean is, they should be placed under the logo like this:
Questions -- Tags -- Users --Space (about the width of the logo)-- Badges -- Unanswered -- Ask Question
As for what the tabs should loo like, I think they should look like a rectangle, I think the color should be light brown.
Background Color
I think the back ground color should be beige. Perhaps a color a yellowish color which you may sometimes find in a Quran:
as for the:
Voting Buttons
I believe yasar11732 'syasar11732 's suggestion is excellent for the design of the voting buttons:
