Allow us to put a text file on the face and back of cards. Many games that use cards are of the "pull one from the deck and read it" variety. Some have a common back to them, but not all do. Limiting them to only graphics makes it tedious for the GM to create the deck. Often simple text will do.
You can create the card image in programs like Gimp (which is free) and just upload the image. You can also use my Card Creator if you like ( <a href="http://www.geeksville.us/swcard.php" rel="nofollow">http://www.geeksville.us/swcard.php</a> ).