ESPN3.com has crashed during the South Africa v. Mexico opener. Apparently there was a huge overload of streams on their servers. Try the recommendations below for alternatives.
I'm a big fan of South Africa hosting this year's World Cup. Unfortunately for U.S based fans, most of the games will have start times when most of them are holed up at work.
For those of you with decent internet connections in the workplace, ESPN3.com offers the best alternative to watching it on TV. The former ESPN 360 site, can only be accessed if your home internet serivce provider has signed up for the paid ESPN service. If you have Verizon Fios, you are good to go, but if you have Cablevision, the parent company of Newsday, you need to look at other alternatives.
Ilemi.com should be the fist place you head to if ESPN3.com isn't working. Their free live streams comes from boradcasts across the world, so the commentators probably won't be speaking english. The good news is some of their streams are in HD and hold up pretty well even to high congestion.
The big name in live streaming is Justin.tv. Chances are they'll have every aired World Cup game live, but their streams tend to get pretty choppy once the requests start pouring in.