Hi- First of all, it might be nice to get an idea of what kind of flowers you would like to use. Blue flowers would limit your choices to very few, for example. You can look up flowers that are a certain color and/or available during a certain month here: http://www.blissweddings.com/weddingfloral
If you’re not set on having blue flowers for sure, you can also use that same website to look up flower colors that will go well with blue and white. Also, some of the bulk flower websites have pre-made arrangements in colors. Check out blue arrangements at Fifty Flowers, for example, here: http://www.fiftyflowers.com/flowers/ArrangementsTableCenterpiecesColorsPurpleandBlueCenterpieces_380.htm This eliminates the difficulties of DIY also. You can get tall containers for these arrangements that will bring some height to the display at the front of the church.
Some ideas I had while browsing through were: Hyacinths in pots placed in large white urns or in modern loooking pots that have been painted white. This would also be very easy on the DIY factor. White roses and blue hydrangea would look great. So would blue delphinium. Irises are a modern looking flower that would also be beautiful and could look great arranged in tall, square glass vases with white stones in the bottom or in a vertical white vase. Blue allium are tall and would look great arranged in the same way. Statice is also inexpensive and hardy and good to mix in with other flowers. Here are some images that I found by searching in google images for the names of these flowers and "arrangement" or "altar arrangement": http://www.afragrantoffering.com/images/Ceremonies/popup/2184c.jpg http://www.dkimages.com/discover/previews/868/867382.JPG http://www.fromyouflowers.com/images/products/new_large/TF146-1.jpg http://bloomeryweddings.com/blog/images/may06-3.jpg http://bloomeryweddings.com/blog/images/may06-5.jpg
http://bp2.blogger.com/_K4rjb6fAQxg/Rg0qfROu0gI/AAAAAAAAAbE/wWPK-HNepeM/s1600/calla%2Blilies%2Bin%2Babundance.jpg (sub in branches with blue flowers for white branches in vases)
Also, you can do something like preserved eucalyptus in large urns or modern, tall vases: http://content.costco.com/Images/Content/Product/144923.jpg Or, you could do a white manzanita branch hung with blue carnation or hydrangea pomanders (look at this pic, but picture the flowers as blue): http://i231.photobucket.com/albums/ee299/loveandsplendor/dpweb0009.jpg
Or you could get beautiful, tall blue glass vases and then just arrange a few lillies, calla lillies, or white irises in them and have a very modern look.
Once you have an idea of your flower types (again, these can be limited by color, availability by season, price), then just do a bunch of google image searche. Sorry to write a book, but hope this helps?