Rundown of interactive mapping sites I've come across, primarily for mapping running (or other exercise) track data using either Google Earth or Microsoft Virtual Earth/Live Maps... (no, I haven't seen one using Yahoo Maps yet). Some require you to draw/trace the route, others allow upload of GPX, KML or other GPS-format data.
Includes MapMyRun, MapMyRide and MapMyTri. Uses Google Maps to draw routes, enter training data and search for others. Imports Gpx and from gmap-pedometer. Exports to Kmz. 5 star favourite.
The original (as far as I'm concerned) - if there was a site around before this one, I didn't find it.
Focussed on GPS data integration using Google Earth maps - since I don't have any toys, haven't really used it. Apparently has lots of 'analysis' features for your data & fitness.
Uses Microsoft Virtual Earth. Exports to Gpx and Kml.
Not so much a website, but a piece of software to manage maps (see NYC below)
ninemsn's rip-off site
Rip-off of my favourite site (above) at mapmyfitness.ninemsn.com.au - slow maps and pretty basic functionality.
In German, but you get the idea...
Great URL but seems relatively new (ie. very few runs in the database)... uses Google Maps.
and for watching only
Tour de France map - the BBC always does great stuff on the web.
New York City Marathon
NYC marathon simlator requires Java, and provided by Sportsim (who have open-sourced their software as CompareTracks - see above).
...and "sorta" related
RunPix doesn't have an interactive map, but does do 'race statistics visualization', including a static map of where you were on the course when the leaders finished.