Csilla found this neat little Excel add-in that converts a table from a spreadsheet to Latex in a simple click. Here is the link:
All you have to do it download the file and execute it. It will install itself in the "add-in" tab in Excel.
What is really good about is that it handles merged columns, alignment and font styles automatically. However, it does not support merged rows, lines, and alignment of numbers on the decimal (it is a requirement in certain journals).