As much as I hate to suggest axing players on the basis of a single performance (Although of course it is more than just one), it has to be done. Bell and Collingwood should be the ones to go. Treat them like Strauss was - except only let them back in when they sparkle in domestic cricket.
As for replacements, well Key is averaging just under 50 and has international experience as well as being one of the best in the world at facing pace bowling, making him an excellent proposition for the South African series. Matt Prior is the highest scorer in First Class cricket and reluctantly I'd be willing to have him back, although I hate the continual change of keepers. In fact Read's also been doing fantastically well. Like Prior, Bopara's also already scored over 500 runs so is a good proposition but again like Prior it is possibly too soon for him to return. Luke Wright is doing well this season but he needs to improve his consistency in First Class cricket as his averages are still way below par. Definitely one for the future.
While Key would be my first choice, David Sales is my second. He averages around 40 but that's hurt by his poor start to his career. In reality he averages around 50. Here are his stats for the last three country seasons as well as hundereds/fifties. This season he is also doing brilliantly while it should be noted he is a big scorer - one of the few Englishmen around nowadays to have scored a 300.
2005 - 47.86 3/6
2006 - 48 2/5
2007 - 55.36, 3/7