If you want something that just works in Google Spreadsheets (as the title suggests), you can use open-ended ranges:
=SUM(A2:A)
In Excel, you can specify the maximum rows for that version; for example, for 2007 and 2010:
=SUM(A2:A1048576)
This will work in Google Spreadsheets as well, and is beyond the current theoretical row limit in GSheets (400000)*.
Edit: *The quoted limit of the new version of Sheets is actually now 2 million cells.