A big flyin - kick in the face, that works! Or you could try accurate straight punches and good movement...
What immediately stops a rush like that is moving sideways while you back up. If you take one step back, he'll just take one more forward. If you take one back and then one to the side (preferably to your right, if he's right handed), he'll be "derailed", off balance and sideways, giving you plenty opportunities to smash his nose in with a straight right / left hook combo. I tell you it works like a charm. There are several other things to do, depending on how experienced you are and how well you are at estimating distance. If you are pretty good at this and have decent footwork, you can back up just enough so his swings miss, and since straight punches have more reach than windmill shots, you'll be able to land yours while he misses.. basically what Amy said. If he's shorter than you, the above is even easier to execute. Always keep your hands up in case you misjudge distance... but if you're more than, say, two inches taller, you can keep one arm out to sort of block him/annoy him, while using your feet if he suddenly charges at you. That works really well.. Wladimir Klitschko does it all the time. However, if you're not much rangier, it can be catastrophic to do that... watch the end of Lewis vs Rahman II for a graphic illustration.
i wish someone had told miguel cotto this before saturday night, so i wouldn't have had to sport this extremely gay avatar
The best way to cease somebody that's swinging wildy is use straight shots and stop their momentum by trying to "hold your ground more" try not to back off so much, Instead of backward movement concentrate on more side movement/footwork. And your best friend would be clean countershots to the face. But there are alot of other ways, boxing is alot more than X and Os, just see what works for you best.....
chances are if they are swinging wildly then they are off balance. try to slip or weave a punch, preferably a right, then step in at an angle with your left and deliver a nice hard shot to their liver. this will soften them right up and they will think twice about coming on all crazy like that. i used to spar a guy who would always do that. after the first time, he got mad and come even harder. i did it again and then he learned to box right. my trainer later laughingly said that he thought the guy had learned his lesson