Another misunderstanding. The tax bracket that you're "in" isn't applied to your entire income. There is no way to keep more money in your pocket after taxes by giving it away to charity (well, unless I guess the charity is crooked and passes the money back to you through an offshore bank account, but that would be an illegal tax shelter).
In other words, if we're right at the top of the 25% tax bracket and the $10k raise bumped us into the next bracket...just for the sake of hyperbole let's say that this was an imaginary 80% bracket...the 80% would ONLY be assessed on the amount of money we made above the 25% bracket. In other words, the $10k.
So if we held onto the raise, we would still pocket $2k over what we did last year. If we gave it to charity, we would get to donate the full $10k...and pay the same taxes as last year, and have no additional money in our pocket from the raise.
Our charitable gift still cost us $2k, even with a ridiculous 80% tax rate. Top rate is only 35% right now (we'll see what happens in January).