Roosters are an integral part of most flocks of chickens, and some people find their vocalizations charming and enjoyable, while others disagree. There are a number of ways you can reduce the amount of time a rooster spends crowing, which ought to keep the neighbors and any light sleepers in your house satisfied.
Be aware that it's pretty much impossible to get a rooster to stop crowing altogether; the most you (and any complainers) can hope for is making your rooster less bothersome (rather than altogether quiet). You can learn more about how to properly care for your pet with the excellent Chicken Keeping Secrets.
Get him some girlfriends. Some roosters vocalize because they aren't satisfied with the size of their flock. If you give him a few more hens to boss around, a rooster may calm down, and spend more time directing the ladies, and less time trolling for more. It's also important to let your rooster mingle freely with the hens; if separated, he may start to crow even more.
Look out for rivals. If you have multiple roosters, keep them well apart, and if your neighbors have a rooster, consider setting up designated areas for each rooster and his flock to reduce conflict.
Confuse your rooster. Roosters have a very finely tuned internal clock, and they crow as they sense daylight approaching. If you're so inclined, you can actually track your rooster's crowing through the year, and you will notice that the time of crowing shifts in response to seasonal changes.
However, you can trick your rooster's internal clock with the use of an artificial light source and an enclosed chicken house. When you bring your chickens into your enclosed chicken house for the evening, use a light to extend the "daylight," tricking the chickens into thinking it's light when it is actually dark outside. Turn the light off before you go to bed.
In the morning, the chickens will think it is earlier than it is because the chicken house is still dark. Therefore, your rooster may be confused enough to wait to crow until you let the chickens out.
Feed him. If you distract your rooster with foods that require some effort to eat, you may be able to get him to start crowing later in the day. Corncobs and puzzle cubes of food like those used to train dogs can be useful for this. Toss the food in at the end of the night, and consider hiding it under some straw so that it won't be found until the rooster starts stirring. If you're lucky, your rooster will be diverted by the food.
Enrich his environment. Contrary to popular belief, chickens are actually quite intelligent animals, and they can get bored, just like everyone else. Your rooster may be crowing out of restlessness or boredom. Try mixing things up in the chicken coop with toys, new perches, and cubbyholes to explore, and move things around periodically so that the environment doesn't remain static.
Your rooster may become so busy exploring the environment and checking for hazards to the flock that he will take a break from crowing.
Keeping a rooster quiet can be a challenge, as some roosters simply have a need to crow, no matter what you do. However, these tips should make the task a little simpler, and they will also demonstrate a good faith effort on your part if the neighbors come around to complain.
If your rooster is causing neighborhood conflict, you may find that reaching out to your neighbors resolves the issue, whether or not you can control your rooster. Offer them eggs or the loan of the flock for a few hours to get rid of garden pests, and be sure to be friendly with the neighbors to cultivate good relations.