Even if Roll20 features video and voice chat, it also has a text-chat window with some good features: speaking of the latter, I'd like to suggest that when a player submits something in the text-chat window, the message appears with a thumbnail of her character's portrait. This looks nice in VTTs, and additionally it helps to quickly identify what player and what character is making dice rolls, typing what she's saying or doing, etc.
This feature could be optional, subjected to be enabled or disabled by the host for people not wanting to see character portraits - thumbnails in a given game.