The deal: The $623 round-trip special airfare includes taxes and fees so there are no hidden extras. The fine print for this deal says the lowest rate applies to nonstop flights to and from Narita International Airport (NRT) Mondays through Thursdays (though I found the rate available on a Saturday; see below). Note that you can't accrue miles on these flights if you're enrolled in the airline's KrisFlyer rewards program, and no refunds or changes are allowed once you reserve.
When: The offer is good for travel now through March 26, but you must book by 8:59 p.m. PST Feb. 8. Again, with such a cheap price, I expect seats to vanish before Feb. 8. (Note: The website says the offer is good for travel through March 24, but a spokesman from Singapore Airlines confirms the deal is good for travel through March 26, and I was able to confirm this by testing the date online.)
Tested: The rate is available on the Web only. I went online to the Singapore Airlines website and found the rate available from Los Angeles on Feb. 8 and returning Feb. 22. I checked comparative rates for the same dates on Kayak.com and found the cheapest flights about $200 more.