Turbine has announced the availability of a web-based PvP leaderboard to coincide with the release of Module 3: The Demon Sands for Dungeons & Dragons Online: Stormreach. A little something about how your character's rating is calculated:
The system DDO uses to calculate PvP Ratings is based on the popular ELO rating system. Everyone starts out with a rating of 1000, and your rating goes up when you win and down when you lose. Your actual performance versus your expected performance determines the exact amount of rating points you gain or lose in a match.
If that last sentence was a little unclear, here's a little more info: When you participate in a PvP match, the system looks at your rating, your team's rating, and the opposing team's rating in order to determine how likely you are to win (expressed as a percentage). If you and your team have a higher rating than your opponents, then the system expects you to win. Conversely, if you and your team have a lower rating than your opponents, then the system expects you to lose. If everyone has the same rating, then both sides have an expected 50% chance of winning.