Delta is offering flights from Denver or Phoenix (DEN, PHX) to London, Amsterdam, and possibly other destinations in Europe for 44,000 SkyMiles plus taxes, with a connection. Flights are from September to November. Use the Delta fare calendar (links) to pull up the deal on Delta’s site.
Note: Additional Taxes and Fees are required when booking with SkyMiles. Taxes will vary depending on the Destination. London has the highest taxes and fees (about +$210). Amsterdam’s taxes and fees are about +$73.