Lots of different answers here. I find this topic very interesting. I've seen fast race winning cars with one fan, no fans and two fans on the top of the engine. If you search on here you will find a lot of interesting information.
Myself I run a cooling duct on my hood that aims at the back two cylinders. My ductwork has a small piece of tin glue to it that acts as a louver. Per the rulebook you are allowed this as long as it does not exceed 3/8th inches tall.
I also have a 4 inch bulge pump fan bolted to the firewall behind the air filters that blows air across the backside of the engine. This was an idea I had found on here and I have to say really works well. If you do this, keep in mind that you are not allowed to blow any air into the carbs per the rulebook, so mount it in a way that is very obvious that you are not doing so. I leave this fan on all race long.
I also have the standard bumper air duct on the drivers side with a tube pointed just underneath the headers.
I have the standard old style Setrab oil cooler with a fan. The fan only works well under caution or when the car is stopped.
I've have since seen the new and improved top end fan setup that Hank Scott is selling and I think its the bomb. Much wider than the old fans, it covers all of the fins and more on the top of the engine. Plus you do not need to cut holes in the hood either. The brackets are machined to bolt to the valve cover. Its a beautiful setup. I don't have these yet.
http://shop.rrcperformanceengines.com/product-p/rrc-topfankit.htmMy setup works well for the time being though.