This isn't a terribly exciting post--what I'll mostly be telling you is that both candidates have approximately the same foreign policy plans.
The Washington Post provides an excellent summary.
Trade: McCain wants more Free Trade Agreements, Obama doesn't. That said, the Democratic majority in congress wouldn't let McCain sign a free trade agreement with North Carolina, so none of that is going to happen in the near future, anyway.
Iraq: Notable differences here include rhetoric, largely, but not much else. McCain thinks Iraq is a battleground for terror, Obama thinks it's a distraction. McCain thinks the surge worked, Obama... didn't, but then quietly stopped commenting on it when he saw the polls were going the wrong way. Obama wants a 16-month withdrawal timeline, McCain... wanted to stay long-term (like South Korea, Germany, etc), but quickly voiced his support for an Iraqi-proposed 2011 deadline for withdrawal.
Iran and Russia: John McCain's unmasked hate for both countries means diplomatic relations would sour. McCain wants to even boot Russia from the G8, push hard for expansion of NATO, and generally relegate Russia to a permanently castrated former power. Obama wants to hold hands and talk. It's actually somewhat unclear what's a better idea, as far as I can tell.
Afghanistan: Both want to add 2 combat brigades to Iraq, and use their fresh mandate as a new president to improve ties with Pakistan, helping build Pakistan's economy and democracy. Interestingly, both support attacks into Waziristan without consulting Pakistan, first. While I may have a lot of criticisms of such a seemingly mutually undermining policy package, I'll save that for later.
Georgia: Both supported Georgia in its war with Russia, but both are letting it fade into the background.
Energy Security: They both want it, neither will get it. Really, the way to be energy-secure in the near term is to mandate CO2 catchers on power plants and use clean coal--we've got lots of it, and it's really darn cheap. But the word "coal" terrifies people. McCain wants more drilling, but probably wouldn't get any more than he already got in this last year, so both would be pushing renewable energy, electric cars, etc. It's a bit more complicated as to exactly what tax breaks and incentives and subsidies would go where, but it'll mostly work out in the wash.
Ethics: Both want to close Guantanamo Bay, end torture as a US-sponsored practice, and repeal other nastier aspects of the Bush regime. Bravo, gentlemen.
Ground forces: Both want to increase them, but with what money, and what recruits? The Iraq war has sucked the country dry of potential warriors and has crushed demand. Maybe their charm and charisma can lure more young rural kids into the armed forces.
Climate change: Both want to fight it. Hello, Kyoto; goodbye, US manufacturing industry.
So if you're sweating foreign policy, don't. It'll mostly be the same either way. And if the Democrats get their unbreakable majority in Senate, which is possible, then the president (either way) won't do much but hold pom poms or pitchforks for whatever they decide they're doing.