Found this over at Slickdeals. I've already purchased 2400 points for $10+tax. Not sure how much longer it will work. All credit goes to akravator ar Slickdeals.

http://slickdeals.net/f/6050586-Xbox...0-Points-for-5

Xbox Live Microsoft 1200 Points for $5
The Microsoft Store is selling the 1200 points card for 14.99 - 10.00 (via code) = 4.99 + tax.
The $10 off code applies to the entire order so buying two cards at once costs 20. It can also be used on 1200+ points cards. Clearly, it is best to just buy one 1200 card at a time.

It took me about 15 minutes to get an email and the codes are available in the downloads section of your MS account profile.

1200 Points
You'll have to search the thread for codes, but this one (XboxEMWAo73d7ehgn) worked twice for me.