Selecting whole column except first X (header) cells in Excel

Click on the first cell you want to be selected and then press Ctrl + Shift + ↓ to select a block of non-blank cells, or a block of blank cells (including the first non-blank cell below it), downwards.  Press again to extend the selection through further blocks.

This may cause the top of the worksheet to scroll off the screen.  Press Ctrl+Backspace to scroll back up quickly.

Universal

=SUM(A2:INDEX(A:A, ROWS(A:A)))

or

=SUM(A:A) – A1

Both will return summary for "column A", except for header in A1

You can simply use the Name box, to the left of the Formula bar, and type the cell range you want selected. Once selected, you can also name this range so that you can use it's name as a reference in formulas and functions.