Keep politics on the agenda. I mean talk about it, make it a part of normal conversation for positive reenforcement. Politics will creep in, but keeping it positive and light should help (but won't prevent) to keep bad feelings from taking dominance. You're a team, play for the team.

EDIT: On some more reflection: Try to honestly assess yourself and how YOU interact with other people. Are you a positive influence? Do you facilitate cooperation and openness? You, as a founder, are a significant (if not the primary) role model in your company.

The highest impact way to affect the politics or lack thereof of an organization is through hiring.

Interview wisely. If there are any questions about character or personality, axe them immediately. Even if they are amazing engineers or fill an immediate need -- if there is a whiff of a doubt, do not hire.

Always optimize to avoid false positives, and accept the fact that you will end up with false negatives through the process.

Don't work with anyone. If you do, don't let anyone listen to anyone except his/her direct boss and don't let anyone talk to anyone except who he or she directly manages. Seriously.

As soon as you have multiple people, you're going to make decisions that someone doesn't like. Politics is how decisions that aren't completely top-down get made and implemented (or not).

Don't tolerate it. If someone is going off the political deep-end, then let them go (in a legal way). You might think doing so could cause things to get worse, but, in many instances, the remaining team will breathe a sigh of relief once the source of negative energy is gone. Just my two cents.

Keep the company flat!! I think most of it depends on the org structure of the company.

I second this. I work at a small flat fairly flat company (owner -> experienced programmers -> inexperienced programmers) and it doesn't feel like there's any politics at all. People separate into their project teams obviously, since you talk to them more, and dealing with large clients has a lot of annoying bureaucracy on their end, but otherwise it works fine.

Another thing to get rid of politics is to make it that there's nothing to be political about. "Politics is the process by which groups of people make decisions on who gets what" or "social relations involving authority or power" [wikipedia]. If you have things to decide about, authority to hand out, your going to get politics! Politics is also a bit about gaming the system. Don't have a system to game!

People will start getting political when they start running into frustrations (or see opportunities) where politics will benefit them or their team in some way. Also making everyone feel like they're on the same 'team' can also help with getting rid of politics, although you have to have a small company to do that.

Don't hire many people, and when you do, don't hire people prone to politics.

How do you recognize people prone to politics?

Require employees to watch powerpoint presentations about it. If that doesn't stop it, nothing will.

You can't - it's called human nature.