Google Directions. Enter Start and Destination and click for directions. Configurable for multiple countries and Google Map options including: traffic, map type, overview, photos, wikipedia & logo. A web part for SP 2007/2010 and other SharePoint v3/v4 based technologies.

GMap.NET is great and Powerful, Free, cross platform, open source .NET control. Enable use routing, geocoding and maps from Google, Yahoo!, Bing, OpenStreetMap, ArcGIS, Pergo, SigPac, Yandex, Mapy.cz in Windows Forms & Presentation, supports caching and runs on windows mobile!