How can I set a keyboard shortcut to switch between Excel tabs?

I don't believe Excel has a keyboard shortcut for toggling between sheets. In Excel 2007 & 2010, as a non-VBA workaround, you can create a window for each sheet that you're working on.

How..

Let's say you were working on Sheet1 and Sheet10.

1. Select Sheet10 and press Alt+W, N. This creates another window where Sheet10 is active. Note that at the top of the window, the file name now has a :2 after it, like so:

   

2. Press ALT+Tab to go back to the first window, and highlight Sheet1. Note that the first window now has a :1 after the file name at the top.

   

You can just use good old ALT+Tab to go back and forth between the two sheets.

Note that you're not creating another instance of Excel, just a separate view for each sheet you need. So you can still add cell references, and pressing CTRL+S in either window updates the file. If you want to work on another sheet, either change the active worksheet on one of the windows, or spawn another one.

CTRL+W closes a window.

Pressing CTRL+G will allow you to type in the tab & cell number you want to go to. For example, in Kaze's example spreadsheet above, if you start with the "Sheet10" tab selected, you can press CTRL+G, and in the window that pops up, type the following:

'Sheet9'!A1

Press "OK", and it will bring you to that sheet & cell. After you've done that once, you can simply double-click the recent links you've gone to, instead of typing in the whole link.