I found this useful article which describes some some keyboard shortcuts in the wiki, but table cells are special: pressing TAB jumps to the next cell and does not indent (luckily).
However, indenting in table cells (instead of using spaces...) would be very useful. In Microsoft Office (using 2007 here) it's CTRL+ALT+TAB to indent more and CTRL+ALT+SHIFT+TAB to indent less. True, the latter is really hard to press, but it works.
Can this be done right now or can it be added (must not be the same shortcuts).