You can try using Qik with the person you want to chat with. Just install the client on both your Evo and on the desktop where you want to chat. edit: there is no desktop client. my bad.
Formerly you could use Fring to video call over Skype, however that functionality was removed after Skype forced Fring to stop using the Skype network. Now Fring only works phone-to-phone as far as I can tell.
At the moment there don’t seem to be many solutions for chatting phone-to-computer. Skype have announced that they will bring video chat to the Android platform soon, and considering iOS4 is doing video-calling in a big way it wont be long before video calling apps are coming out.