A few years ago, SimGoober released a great pack of churches (and a synagogue). It's nice, but I wish there were a couple more.
I recently stumbled upon these beautiful church examples from the Philippines which would make beautiful pieces of church buildings in the game:
http://upload.wikimedia.org/wikipedia/commons/b/bd/PagSanJoseChurch.jpg
http://upload.wikimedia.org/wikipedia/commons/7/70/Pagadian_Cathedral.jpg
Here's one more (the Mormon church designs are particularly very nice IMO, and all of Goober's churches are more traditional designs): http://www.cswnet.com/~berryvil/church.gif
I also think there need to be more mosques in game as well (in fact, I do not know of any created for SC4!) for complete realism. Here's a smaller one I think would do well in the game setting, an example I have seen before on the campus of Arizona State University:
http://www.whyislam.org/wp-content/uploads/1970/01/ArizonaMosque.jpg (IRL the minaret you see there had to be dismantled at the top for safety concerns but is now being rebuilt)
http://www.statepress.com/wp-content/uploads/2010/08/8.24-Mosque.jpg
http://commondatastorage.googleapis.com/static.panoramio.com/photos/original/5834307.jpg
One of the kind of interesting things about this particular mosque is that nearby, there is a small corner commercial services space with the same blue tile theme and white mission arches that has a halal foods shop and Mediterranean kitchen. (hint: 3x1 or 3x2 CS$$ plop?)
I think perhaps there should be one or two more mosque styles to provide variety. Here's one in Qatar that might be good for a 2x1 or 2x2 lot:
http://www.burlite.co.uk/image/pic7.jpg
One in Oman that might be better suited to a rectangular lot type (2x1 or 3x2?):
http://www.traveladventures.org/continents/asia/images/qurayat06.jpg
My last request here are some wall components to create subdivisions: curved wall entrance piece, straight piece, a corner piece, diagonal entrance marker piece, maybe a smaller entrance bookend piece. In Arizona, there are so many subdivisions, and to date I have not found a nice wall set. I think two or three different styles to choose from would be interesting as well.
I'm sorry if I'm asking too much, but I'm merely pointing out some things that I'd like to see expanded or added (surprisingly I know of no mosques for SC4, especially ones that could fit well into urban or small areas without being TOO flashy).