MapPoint Web Service, MapQuest Business API, or roll-your-own with a real ArcServ or Autodesk MapServer.

All cost money and (most importantly) provide unfettered access to multipoint routing and driving distance calculations; entry level for the web APIs is a solid $5K/year commitment. The platform solutions (as I said before) reach the $30K-50K range, but offer unlimited customizability.

When I priced it out over a year ago, MapQuest worked out to be about 25% less than MapPoint, but MS may have revised their pricing since then to be more competitive. Of course, MS' SOAP API is a bit easier to use.

-Matt

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PMPVOWs.com Lead Programmer, MLSNI IDX/VOW solution provider