I started looking at GoogleMaps solutions...
And decided on this one -http://dotnet.sys-con.com/node/171162 - simply because I liked the article format and because I thought the code format (custom control) looked easiest to integrate and maintain.
Sadly though the code is a bit out of date (it dates back to an old v1 beta API!) so there are some fixes to do:
- I fixed the addOverlays and reOrderOverlays bugs - see the comments on that article
- I fixed the MAP_TYPE type bugs
If there are other fixes then refer here for some inspiration - http://code.google.com/apis/maps/documentation/upgrade.html#MapTypeNames
There are other implementations around - e.g. http://www.shabdar.org/google-maps-user-control-for-ASP-Net-part1.html - if maintenance proves too hard then I may switch to there!