Well for starters, you'll need the Ninetales. Good luck doing sun without it.
Sun teams are naturally weak to Tyranitar, by virtue of Ninetales inability to do anything to it. Throwing in a Fighting-type like Terrakion works brilliantly for scaring out Tyranitars. A fighting-type also works well to eliminate Heatran, who is a very big thorn for sun teams.
Sun teams also hate entry hazards, especially Stealth Rock. In weather wars, having a rapid spinner is important because Ninetales will have to enter the battlefield a lot. Forretress is a good rapid spinner for sun teams. The boost to Fire-type moves doesn't matter too much to it; they would've OHKOed him regardless of weather.
Sun's best sweeper is currently Chlorophyll Venusaur, who is incredibly difficult to outspeed and very powerful after a growth boost, especially now that Giga Drain is legal with it.
This should give you a bit of a start.