Too many toys? Kid can't keep his room clean because there's just too much stuff? Here are a few possible solutions.
1. Donate. If you can give a convincing enough speech about privilege and want, you can have your child cheerfully filling up boxes with his discarded playthings to give to Good Will. If, however, your child really feels that he can't let go of his possessions of his own accord, remember that he has to sleep sometime! When the child is asleep, away, or looking in the other direction, choose toys to get rid of that you know are not favorites, that will not be missed. Use your mommy discernment. As long as you know you are choosing things that are truly outgrown or unloved, it won't backfire, but keep the box of toys to donate in the garage for a week or two just to make sure you didn't accidentally scoop up something he can't live without.
2. Rotate. Get a big box that will fit lots of toys, and put a big pile of toys inside to wait their turn in the garage. Explain the rotation system to the child, so that she understands the stored toys will not be gone forever, but can be retrieved (if she wants) on a certain date, and put the date on a calendar, even, if she's worried about forgetting about them. Let her fill up the box, then give a reward (like making cookies, playing a game) when the box is full and in the garage.
3. Delegate. If all the toys have been gotten rid of or rotated out into the garage, and the room still isn't as clean as you'd like, try this. Put her in charge of cleaning up her space. The realism of this enterprise depends on the kid's age and maturity. We put our seven-year-old son in charge of cleaning his room recently, and he does a reasonable job of it. Set a time limit for your child to finish, and then at the end of the time, go in with a garbage bag and pick up whatever isn't put away. Tell her that next time (next Friday or Sunday or whatever day is clean-up day) you will put everything back on the floor from the garbage bag and she can try again.
Now I personally do not care if the kid's room is clean on a regular basis. I don't care if he leaves out his legos and dominoes and all his castles and rolls around in his books and blocks and whatnot. The only time Benny has to clean is every two weeks before the cleaning lady comes, and the garbage bag trick works nicely to get this accomplished. I'm not sure if everything gets put away exactly properly, and I don't really care, as long as the floor is empty and the cleaning cleaning ladies can get at the surfaces. He does have a place for everything, but everything isn't always in its place. I'm not a mother who demands the matchbox cars be neatly stacked in the box labelled "Cars!" or anything. But I do want him to learn to keep his room comfortable, so he can see what he has, and find what he needs.
His three-year-old sister, on the other hand, has never picked up a toy in her life. Oops... ;D