Excel cannot directly export charts or Save As in other image formats, but with a simple macro one can export charts in PNG format. This format is great for including charts in LaTeX documents with \includegraphics{chart.png}.

The macro can be stored in the personal macro file PERSONAL.XLSB. Excel 2010 places the file in the following location: C:\Users\yourusername\AppData\Roaming\Microsoft\Excel\XLSTART

This file is hidden when first starting Excel. To unhide, perform the following steps.

+ View -> Unhide
    + Unhide personal macros file.

You can now select the View -> Macro or the Developer -> Macros menu items to create a new macro. The macro for saving the generated PNG files is as follows:

Sub Export_ActiveChart_as_PNG()
'
' Export_ActiveChart_as_PNG Macro
' Export Active Chart as PNG
'
        ActiveChart.Export Filename:="C:\path\to\save\excelcharts\" & ActiveSheet.Name & ".png", Filtername:="PNG"

End Sub

The generated PNG file can now be used in tex documents as usual.

Today, however, I found another alternative, but it doesn't work as well.

Save chart as PDF

Excel 2010 provides a Save As option that can save the active chart as a PDF file. The file can be used directly with \includegraphics{chart.pdf} but the resulting PDF has a significant white margin all around that would have to be cropped for better results. Cropping a PDF without the full version of Acrobat can be a problem, so the PNG route works better, in my opinion.