I would like to add something like a sun into my map. Is there a way to attach a circular flare effect to a light, or place an object that looks like a sun?

I beleive you have to add a sun effect to your sky file like so:

SunInfo()
{
Angle(150.000000, 0.000000);
Color(70, 78, 80);
Texture("");
Degree(0.000000);
BackAngle(210, 0.000000);
BackColor(0, 0, 0);
BackDegree(0.000000);
}

then add a directional light in ZE and label it sun and position it in the place of the suninfo. So it'll cast shadows.