Chris Moody has a good breakdown of how much the presidential contenders and their running-mates paid in taxes last year, and... how generous they were.
Tax Rate:
1. Joe Biden 23%
2. Barack Obama 20.5%
3. Paul Ryan 20%
4. Mitt Romney 14.1%
It's important to note that Romney paid taxes off his investments, and since investments are taxed at a lower rate than income, he incurs the 14.1%.
Romney was also the most generous.
Charitable Donations:
1. Mitt Romney 29.35%
2. Barack Obama 22%
3. Paul Ryan 4%
4. Joe Biden 1.46%