[nxn]

ExtJS's set of grid panels was just about the most impressive one I've seen thus far (tree grids, group grids, paging grids, features for filtering/searching, sorting, hide/show columns, binding to xml/json/direct, etc). Though it would probably huge overkill to tie yourself into the whole framework just for one widget.

Examples: http://www.sencha.com/products/extjs/examples/#sample-2

[edtechdev]

yeah see also dojo's grid (grids I should say, there are several)

jquery.sheet

yui grid

not sure if Google's closure library has a grid control

and of course there are GWT, qooxdoo, etc.

Heres a table comparing javascript frameworks, and there's a row for which have a grid control.