All of these fares are found using airfare metasearch site Momondo:
Airfare Spot: New York, Chicago, and DC – Amsterdam from $386 roundtrip on United for December through March travel excluding holidays.
Copyright: jojjik / 123RF Stock Photo
Airfare Spot: DC, New York, and Chicago – Paris from $416 roundtrip on United for January through March travel.
Airfare Spot: Los Angeles – Tokyo from $446 roundtrip on United for November or January through June travel. (I’m showing a fare a few dollars less, even, because I’m including student travel agency STA Travel in the search.)
You can credit the miles for these trips to Singapore Airlines KrisFlyer and earn more than you would any other way.
While a non-elite MileagePlus member crediting United flights to the revenue-based MileagePlus program will only earn 5 miles per dollar on the cost of the ticket excluding taxes, nearly all United fares earn 100% of flown miles when crediting to Singapore Airlines KrisFlyer (.pdf). That means you earn 5-10 times as many miles with Singapore Airlines KrisFlyer for your trip flying United than you would crediting to MileagePlus.
While Singapore miles do expire after 3 years (not 3 years of inactivity), you can top off a KrisFlyer miles account with transfers from American Express, Chase, Citi, and Starwood.