If you live here in WA, please tell me you already voted (or are doing so TODAY!!!). For those of us who live here and have already done our civic duty, there's a website where you can check to see if your ballot was received and it's status (accepted or rejected).
Votewa.gov
Just enter your details on the main page (First, Last, DOB), Then (if you did that correctly), click "Menu", and under "My Ballot", select "Ballot Status". It will give you the date your ballot was received and its status (accepted or rejected). You can also view your past voting history and do other fun(ish) things.
If your ballot was lost or destroyed, you can get a printable online ballot with return instructions (clicking that link will invalidate the one originally mailed to you, so don't do this if you don't need it).
I'm not sure if other states offer this, if you're elsewhere, you'll need to Google it.
Hurray for twenty first century technology!