jExcel is a jQuery plugin to embed a spreadsheet, compatible with Excel, in your browser.
You can load data straight to the table from a JS array, json or even a CSV file. You can copy and paste from or to Excel straight to jExcel.
ParamQuery grid is a lightweight jQuery grid plugin inspired by MS Excel and Google spreadsheet. It's based upon jQueryUI Widget factory which is an excellent design pattern for UI controls with consistent API. It's free to use.
Handsontable is a minimalistic approach to Excel-like table editor in HTML & jQuery. Now with column and row headers.