My office room is in the front of the house and facing south. It gets hot very fast during hot days (even in spring). It is a fairly small room and I have computers there attributing to heat. There's a small double pane window with cloth blinds. There's a central AC but running it full time just cool a small room does not seem very efficient.
What are the ways to reduce amount of heat from the direct sun hitting the wall? Special paint? Drapes? Tent? Fan?
A good deciduous tree helps, but it will take a while for that to work. Just be sure not to plant it too close to the foundation.
Light blocking blinds are very good at blocking both heat and light. This may not be good if you're trying to work in the room.
Insulation helps if you have an attic above, just don't block the ventilation from the soffits.
However, the important thing to realize is that cooling systems spend a significant effort overcoming the heating effects of people themselves. And a couple computers doesn't help. No matter how much you block the outside heat, the heat being generated is still there. Therefore, make sure your vents are adjusted to cool the rooms you use (closing doors also helps), and direct most of your cooling to the upstairs. If that still isn't enough, try a small fan in the doorway blowing in cool air from the floor (which will push out the hot air above).
Edit: Couple other thoughts.
Get an IR thermometer to check all your walls and various other heat sources. You may discover a patch of uninsulated wall or find that the window it letting in more than you thought.
Second, check your thermostat to see if it has a setting for how much the temperature will vary before it cuts on. Mine is an odd key combination that's buried in the back of the manual. If you're going well over an hour between AC cycles, you'll reduce hot spots by reducing this setting.
There are several options.
One of the easiest ways is a shade or awning over the window. (This is why Australian outback homesteads have deep verandahs.)
Another method is an external shutter, but this will reduce the light a lot, as well.
You could also go for a window coating. There are a number to choose from, ranging from an aluminium film to a fine mesh. The goal is to reflect away the heat whilst not losing too much light.
with a small room, it could be very efficient to use a small window A/C unit to localize the cooling and reduce the workload on your main A/C.
as far as i know, the best affordable result is passive solar shading that will use the warmth of the winter sun and rejects it in the summer. the specific design is dependent on your latitude and the method of construction, but it should look something like this, and this sketch can also clear the general idea.
solar passive techniques are the best way to handle this issue, and it will save you a great amount of money for the long run, & don't forget to mention the co2 emissions and environmental impact.
here you can find some reference to a bunch of ideas in this field, and i recommend you to read the passive solar energy book. it is a MUST.
edit:
My office in my old house was on the west side of a brick house. The sun would shine on the bricks all day. The bricks would heat up and make the room warm even when the sun had gone down. I put a ceiling fan in the room. The slight circulation of air in the small room helped tremendously.
Consider window film. There are ones on the market that are UV blocking that will help cut down the heat in the room without affecting how much visible light comes through.
As another strange answer -- consider adding thermal mass. Some solar passive homes use stone or brick, but you can also use large containers of water so the room won't change temperature as fast.
Whatever it takes to shade the wall is the most effective solution. Also use blackout window drapes (when you close them the room is completely dark). Trellis panels with vines, trees or even consider relocating the office to another room.
