I used the Actions Class like many listed above, but what I found helpful was if I need find a relative position from the element I used Firefox Add-On Measurit to get the relative coordinates. For example:
IWebDriver driver = new FirefoxDriver();
driver.Url = @"https://scm.commerceinterface.com/accounts/login/?next=/remittance_center/";
var target = driver.FindElement(By.Id("loginAsEU"));
Actions builder = new Actions(driver);
builder.MoveToElement(target , -375 , -436).Click().Build().Perform();
I got the -375, -436 from clicking on an element and then dragging backwards until I reached the point I needed to click. The coordinates that MeasureIT said I just subtracted. In my example above, the only element I had on the page that was clickable was the "loginAsEu" link. So I started from there.