+1 for textpad
and yes you can replace on more than one line. The older versions used to have multiple lines on their replace dialog box but now the newer just uses one and relies on regex so you can get all the different return characters.
To replace multiple lines just use \n to indicate the line return and yes it does work with html or any other type of ascii file.
If an example will help here's how to remove the quotes from a bunch of strings enclosed in quotes.
"line one"
"line two"
"another line"
"some quotes "inside" of the string"
Edit >> Replace >> Check regular expression
Replace: "\n"
With: \n