Xujiahui metro station is the place to go if you're after game consoles (the Wii is available here in relative abundance), computers, computer accessories, or the like. You'll find pretty much everything electronic there, but the cellphone selection is a bit lacking.

If you're after a new cellphone, go to the Shanghai Railway Station. You can find good deals on secondhand phones as well as new phones (the selection is a mixed bag; you'll find Chinese off-brands mixed with reliable big-name brands like Samsung and Nokia as well as cutting-edge Japanese phones; if you live in North or South America be careful about buying the off-brand phones as most do not support the necessary frequencies for use there. Also, in the secondhand section of the market some of the phones are of dubious origin; CDMA phones may have their ESNs blacklisted in their home countries, but for GSM/3G phones the only issue is an ethical one. Be careful about prices that are too good to be true.