Since the release of Gingerbread, most HTC EVO ROMs have had a built-in method to take screenshots (pwer button + Home). Unfortunately, this leads to turning off the screen or exiting the application you're trying to take a picture of more often than it should. Pictures are also fairly low quality and have to be opened up with a separate app to even view whether you captured what you wanted to.
That's where Screenshot ER for rooted devices come in. It brings a whole new level of functionality to the table by allowing you to take screenshots by shaking your phone (like the ever popular ShootMe) or long pressing the search button.
Once a screenshot is taken, a small thumbnail popup is visible, which you can then choose to save or discard. If you want to keep the image, you can save it in JPEG or PNG format, rotate and flip it, or use your integrated share menu to send it to the world.
Screenshot ER has plenty of other options too and is a pretty darn useful little tool when you want to send high quality pictures of your screen somewhere.
I'd been using ShootMe, which seems to have disappeared from the Market and doesn't have the extra functionality anyway, but I think Screenshot ER is in serious contention to replace it.