*UPDATE 2017-10-12:*

As noted in the comments, there is an even much easier way to do this now!

=TEXT(A1,"ddd")

At some point Google updated the text function to take formatting parameters which makes this a cinch.

The old post from 2011-10-09 follows below and is a great introduction to the

**function. But don't use it for getting the day of week anymore!**

*CHOOSE*Google Spreadsheets has a nifty function named

**which exhibits behavior like the switch statement programmers all know and love. Basically, it allows one to select an action/value based on some input. This is GREAT!**

*CHOOSE*I needed to fill cells with the day of the week given a date. There isn't any built-in function that performs this task in Google Spreadsheets right now. But, we can solve this very easily using the

**function.**

*CHOOSE*=CHOOSE( weekday(H1), "Sun", "Mon", "Tue", "Wed", "Thu", "Fri", "Sat")This formula is very simple:

*The contents of cell H1*holds the date- The function
*weekday*converts that date to a number from 1 through 7 representing the day of the week (Sunday=1) - This value, in turn, is then used by
*CHOOSE*to select which value in the subsequent list to use in the current cell - Voila

E... to the Z.

In this case, we are converting dates to days of the week in the format I wanted. Now we can start getting all fancy. Imagine, instead of days of the week, the list of possible values were different formulas to compute some result. The formula to use depends on the value inserted in the first input to

*CHOOSE*. However, remember that nothing is stopping even this first input from being yet another formula computing a specific result based on the data in particular cells.
With this function, the possibilities are endless!

*Reference:*See the second comment on this blogpost