This trick is so easy and so old that I think everyone knows about it, until I run into somebody who doesn't! So, here's a reminder of a useful trick that's been around for a while, just in case you've never seen it in action or forgotten about it.
To quickly sum values in a row or column, select a blank cell to the right or below the data, respectively. It doesn't have to be the first blank cell, but the cells between the values and the cell must all be blank. Then, click AutoSum on the Standard toolbar and click Enter. In Excel 2007/2010, AutoSum is in the Editing group on the Home tab. Excel will automatically enter the appropriate SUM() function, referencing the values to the left or above. In this case, Excel references all the numeric values until encountering a non-numeric value.
You can also use AutoSum with a subset. To do so, select just the values you want to sum, plus a blank cell for the function. For instance, by selecting cells E6:E4 before clicking AutoSum, the resulting SUM() function references only E4 and E5, instead of evaluating all of the numeric values in column E.
Even when users know about AutoSum, they tend to use it infrequently, but I say, use AutoSum every time you want to enter a SUM0 function.