AT&T's store (of all places) has a deal going on for PS Vita 16GB and 32GB memory cards. Seems to be about 30-40% cheaper than what you find them for most places.

16GB - $30 (after $30 online discount)
http://www.att.com/shop/wireless/acc...ku6170245.html

32GB - $50 (after $50 online discount)
http://www.att.com/shop/wireless/acc...ku6170247.html

Probably won't last very long. Enjoy!