I am holding Circuit City Stock. I understand that they have filed for bankruptcy. When will I be able to claim this loss?

Your stock is not considered to be totally worthless until the company ceases operations. My underatsnding is that Circuit City announced in January that it was suspending operations, so you should be able to take a write-off on your 2009 taxes. Here's an article that discusse how to report this.

Fool.com: When Good Stocks Go Bankrupt [Fool's School Daily Tip] October 24, 2001