Can emacs re-indent a big blob of HTML for me?

By default, when you visit a .html file in Emacs (22 or 23), it will put you in html-mode. That is probably not what you want. You probably want nxml-mode, which is seriously fancy. nxml-mode seems to only come with Emacs 23, although you can download it for earlier versions of emacs from the nXML web site. There is also a Debian and Ubuntu package named nxml-mode. You can enter nxml-mode with:

M-x nxml-mode

You can view nxml mode documentation with:

C-h i g (nxml-mode) RET

All that being said, you will probably have to use something like Tidy to re-format your xhtml example. nxml-mode will get you from

<!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.0 Transitional//EN" "http://www.w3.org/TR/xhtml1/DTD/xhtml1-transitional.dtd">
<html xmlns="http://www.w3.org/1999/xhtml">
  <head></head>
<body>
<table>
  <tr>
<td>blah</td></tr></table>
</body>

to

<!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.0 Transitional//EN" "http://www.w3.org/TR/xhtml1/DTD/xhtml1-transitional.dtd">
<html xmlns="http://www.w3.org/1999/xhtml">
  <head></head>
  <body>
    <table>
      <tr>
    <td>blah</td></tr></table>
</body>
</html>

but I don't see a more general facility to do line breaks on certain xml tags as you want. Note that C-j will insert a new line with proper indentation, so you may be able to do a quick macro or hack up a defun that will do your tables.

http://www.delorie.com/gnu/docs/emacs/emacs_277.html

After selecting the region you want to fix. (To select the whole buffer use C-x h)

C-M-q

Reindent all the lines within one parenthetical grouping(indent-sexp).

C-M-\

Reindent all lines in the region (indent-region).

Tidy can do what you want, but only for whole buffer it seems (and the result is XHTML)

M-x tidy-buffer