This price match worked for me today at Best Buy but your success may vary depending on where you go (sounds like people are having the most luck at BB, so I'd try there first). Credit goes to CAG for finding the deal.
Sears.com had 12 month Xbox Live subscription cards on sale saturday/sunday for $20. They sold out fast but if you print this screen grab up and bring it to BB, they might price match it for you:
http://img683.imageshack.us/img683/260/deale.png
Didn't think I had a chance of getting it myself when they called Sears to confirm but somehow they approved the price match, so I got two 12-month cards for $39.98. Apparently they have some Sherlock Holmes tie-in pack that they're giving out with these which includes a free movie ticket, so make sure you grab one of those too.