What is the quickest way to...

Copy a formula down the whole column?
Select the cell that contains the formula and double-click the small square
on the bottom, right-hand corner of the cell. (It is called the Fill
Handle. Your cursor turns into a skinny Plus sign when it is positioned
over it.) Your formula will be automatically copied over everything below
it, as far down as there is data. (If there is no data in the same column,
the formula is copied as far down as there is data in the columns next to
it.)

Fill in a series of data?
Enter at least two items in a range of cells. Select those cells as a
group and drag the group's fill handle down to fill the column (or drag to
the right to fill the row). This works with many dates, month names, and
numbers, as well as any custom lists you have set up.

Enter the same value into multiple cells?
Select the range of cells, type the value, and press Ctrl+Enter.

Enter values in a specific range of cells?
If you are in the habit of using the Tab key when you enter data, and you
only want to enter data into one specific range of cells, first select the
cells in which you want to enter data. Each time you press Tab, you will
move to the next cell. In other words, if you select cells A1 through D4,
enter data into A4, and press Tab, your cursor moves to B1, staying within
the selected range.

Posted courtesy of Tips.Net