It's easy to find the last cell at the end of a range of data:

1. Click any cell in the data.
2. Press CTRL+END.

If you've formatted some rows or columns beyond the last cell that contains data, Excel selects the last cell that's been formatted.

To select the entire range:

1. Click the first cell in the range.
2. Press CTRL+SHIFT+END.

For more information about quick ways to select data in Excel, type select data in the Office Assistant or on the Answer Wizard tab in the Excel Help window, click Search, and then click "Select text, cells, ranges, rows, and columns."