The following video will show you how to sort the sheet-tabs in alphabetical order in Excel by using ASAP Utilities.
The example in the video show a workbook with several sheets with city-names:

In the Excel menu choose ASAP Utilities » Sheets » Sort all sheets in alphabetical order
Then result will then look like:

Note: This old video is no longer available and will in 2021 be replaced with a new version in a modern version of Excel.