If you are trying to cool a kitchen of any size, an area that receives full sun, or a room that's larger than 300 square feet (which is about 15 feet by 20 feet), you need the power of a large window air conditioner. The best have a minimum of 9,500 Btu, a beefy compressor that blasts a sufficient amount of icy air and a fan that can circulate it through the entire space. Be careful stepping up too much, however, a unit more powerful than 12,000 Btu will require a 220-volt outlet, which means you'll probably need to call an electrician.
If you want to use a regular household outlet but need a large window-mount air conditioner, the Sunpentown WA-1211S (Est. $320) is one of the most powerful available. At 12,000 Btu, reviews say it's an excellent pick for cooling up to 700 square feet quickly. The Sunpentown pulls extra duty as an air purifier (and is the only unit in our report with the option to draw in outdoor air) and also has a dry mode to dehumidify the air without the arctic blast. To cut down on energy costs, the WA-1211S features an energy-saver mode and sleep mode; most say these work well to keep the room cool without spiking the electric bill. A 24-hour timer and fully functional remote control add even more convenience.
For a slightly less powerful unit, reviews say the Frigidaire FRA106CV1 (Est. $310) is a very good option in the large window air conditioner category. Its 24-hour timer can be set in 30-minute increments and the antibacterial mesh filter tilts out for easy cleaning. Owners especially love the remote control's onboard thermostat, which takes the temperature of the room wherever it's sitting to better meet your target temperature for the entire room. The Frigidaire's 60-pound weight adds to an installation that some say is already a bit challenging. A few owners mention that the fan and buttons are noisy enough to be disruptive for sleeping and watching TV.