Perhaps unsurprisingly, the 1600 point card's closest competitors come from Nintendo (people have to play all those copies of New Super Mario Bros. Wii with something after all). In April, the Wii Nunchuk and Remote took the second and third spots, respectively. In March, the second and third spots belonged to the Nunchuk and Wii Motion Plus. The month prior, the card was actually at No. 2, so it seems like Microsoft is doing a pretty brisk business in MS Points.
The question, of course: Just why was everyone stocking up on Microsoft Points? Oh, right.