Buy renewable energy credits (e.g. wind power) equivalent to at least 50% of your electricity usage.
I've switched my power source from Dominion's standard mix of mostly coal-fired and nuclear power to green power, though it was more expensive and a long process. I'd much rather switch my power source directly to green power than to still use coal/nuclear with credits. With the latter, you're not directly reducing your carbon footprint, you're just trying to offset it, a questionable practice.
Wikipedia can give you a quick overview of green power. You can also track my progress in completing the Green Living Challenge.
Points for this action: 10
Total points to date: 85
Points needed to complete Green Living Challenge: 100