To truly solve this dilemma, you have to go back to the root of the problem. Your forced-air AC system is overstretched and the placement of the window in your room (it's probably facing south) are the sources of the problem.
Step 1: Prioritize which rooms really need AC:
Close the central air vents in either the coldest room in your house (by the virtue of forced-air HVAC systems, this most likely will be the room closest to the heater/AC unit.), or rooms that are seldom used (like those extra bathrooms, guest rooms, etc. that aren't really ever used) and don't need to be cooled. If these vents aren't adjustable, then take the vent cover off, put a piece of cardboard into the vent*, and put the vent cover back on.
If you don't need a room cooled/heated to perfect room temperature, then why
pay for waste the energy to do so?
* With this method, you could always cut small holes into the cardboard to restrict airflow (as opposed to entirely stopping it), but the decrease in air entering that room should at least somewhat increase the airflow to your room.
EDIT: After just thinking about using cardboard for a moment, from a fireproof standpoint it would probably be better if you went to Home Depot or Lowes, bought a small sheet metal air duct plate, and using tin snips cut it down to size and used that behind the plate instead of cardboard.
Step 2: Eliminate possible sources of "wasted" AC:
Tint your windows/skylights with a light-blocking product. Leave the shades/blinds/etc closed. Glass acts like a greenhouse, so if you can stop the suns rays from entering the room, then you're less likely to have your AC wasted by the sun's radiant energy.
For bonus points, both of these solutions have the potential to not only
save you money in the long run on utility bills, but they're also
green, environmentally-friendly solutions. It's win-win.
// Me thinks I've spent too much time working on houses... 