Andy Armstrong Wiki Map Widgets that make it incredibly easy for Wiki'ers (is that a word?) to embed maps in Wiki pages.

See the simple markup:

 



    

        [http://www.overwaterlodge.co.uk/ The Overwater Lodge]

    

    

        [http://www.nenthead.com/ The Miners Arms]

    

My suggestions:

1. Use Mapstraction for easy mapping provider switching, including OpenStreetMap support.
2. Support for GeoRSS layers. Easy way to create a large set of markers from a GeoRSS feed (or KML)
3. Static image fallback for users without Javascript/slow connections (since Wiki's are not inherently high-bandwidth users)