The symbol of a fish is often used to represent christianity, and can be called either Icthus, Ixthus and often simply the Jesus Fish.
Here's a small, but nice image of Noah's Ark filled with animals.
Here's an Medieval style, black and white image of a Christian (Catholic) Priest with sacrament.
A beautiful and simple image of the nativity scene, showing Baby Jesus lying in the manger with Mary and Joseph looking lovingly at him.
Golden crown of thorns.
A black bible.
Another clip art of a bible.
The next few are of crosses, this one's a simple silver cross draped with gold fabric.
A small white cross outlined with gold.
This cross decorated with flowers is perfect to represent Easter.
A glowing cross.
And finally a lightly animated gold cross.