It seems that the average going rate at large retail stores, for 1600 XBox Live Marketplace Points Cards, is $25.00. Both EB Games and GameStop have them for $19.99 online. But beware - if you go online to GameStop, even if you enter the FREESHIPALL code to get free shipping - they add a Handling fee of $10... making it a much worse deal than just walking into Target and buying one. Circuit City also has a 1600 card for $19.99 listed online, with local pickup available - hopefully there's no handling fee for that.
You can also just sit in your living room and buy 2000 points for $25 from Microsoft on your Live account. If I did the math right - never guaranteed with me, lol - the prices are the same for the EB/ GS and the MS (for 2,000 points), or .0125 per-point.
I also checked eBay, and very few people seem to be selling the point cards, and there were no better deals, as of this morning. As always, patience is a virtue on eBay and you could make out there... or not.
If anyone sees a sale that is better than .0125 per point - please post here... thanks!