Ojan points out there's a need for a "tab" command, since "indent" doesn't match the behavior of tabbing: http://lists.w3.org/Archives/Public/public-webapps/2012JanMar/0090.html
This needs to behave like indent for lists, but in regular text probably needs to insert something like <span style="white-space:pre-wrap">	</span>, and in tables should tab between cells.
Do we also want an "untab" command that behaves like Shift-Tab? Presumably yes, for table cells at least. How should it behave in regular text? Or lists? LibreOffice Writer behaves oddly.
For the regular text case, matching the behavior of most decent text editors would be *awesome*. Specifically, when the selection covers multiple explicit lines, put a tab at the beginning of each line.
Untab then does the same thing, removing tabs from the beginning of each line that has one.