Excel Sum with Errors

How to do a sum in Microsoft Excel when there is a #N/A field or other such error in the values to be totaled?  There seems to be a ton of posts on the net, but only a few had the simple solution:

SUMIF Function

For example: =SUMIF("A1:A20","<>#N/A")

You can get more complicated with your earlier formulas using ISERROR to avoid the error in the first place, but that's probably more trouble.  If you want to re-produce, you can generate the error value with =NA().