Replace text in multiple files

[lemmas]

Is there a command or two that will replace a string with another string in multiple files at once? I need to change the same text string in a bunch of html files. If I can do it with one or two commands that would be sweet.

Thanks,
Nick

[redhead]

for file in 'ls *.html'; do cat $file |sed 's/some text/some new text/g'>$file.new done