I know that Google Maps has an API that you can use to generate maps for addresses on your site. I've played with it for our church website and wanted to point out that there are definitely problems with the API. When I mapped our church through maps.google.com, I had no problem getting the exact location of our church. When I plugged the address into their API, it generated a pointer about 1 mile south of our church. I needed to use another tool to tweak the numbers and then adjust the cache for that map and the location used.
If you're interested in doing this, I believe that Yahoo! and Google (possibly even MS) provide APIs that can be called with your data. If you use Data Exchange to pull the addresses and then plug those into the API, you can get a pretty good general location for the addresses. Yahoo! may be more accurate in some instances than Google, but all should work. I remember reading a brief article on writing some CLR code in C# to translate SQL Server addresses into the specific codes generated by those APIs. The WEC team has written a wrapper in PHP for Google Maps. You may be able to use some of that code to generate something similar for your site. The great thing about these is that you don't have to upload all of your data to Google/Yahoo!/etc - you just issue the calls and their APIs plot the points appropriately. They should all have good forums to get some assistance when you need it.
I'm not much of a web programmer, but hope that these at least give you some ideas to look at for your web site.
In Him,
-Peter Schott