In Selenium IDE you could simply use getSelectedLabel | locator and that was your currently selected item in the drop down list. Its a bit more of a roundabout way with WedDriver as you can see from the method I have written below:
public string getSelectedLabel(ddlDropListID)
SelectElement selectOption = new SelectElement(ddlDropListID);
selected = selectOption.SelectedOption.Text;
While there is a few more lines of code required, it is a short enough snippet to learn.