For 2008, that's $10,900 on a joint return, $5,550 for a single. For 2009, that's $11,400 on a joint return, $5,700 for a single.
For years, Congress has been talking about a charitable deduction for non-itemizers, but the provision has yet to be passed.
Each dollar you contribute gives you a tax benefit equal to your marginal tax bracket. Let's say you're in the 25% bracket. A $100 contribution saves you $25 dollars in tax. In the 35% bracket, you save $35. The real cost of your donation is only $65.