Metro is about to announce an long list of places where you can buy AND LOAD SmarTrip cards using installed machines. Previously, you could only purchase cards with no value* and then add value at a train station. No longer.
*Correction: Metro now says the $10 cards have been available since Dec. ($5 for the card, $5 value). Thanks "emmzee" for the heads up. The add value terminals are new, Metro says.