YouTube makes it easy to find 3D videos to watch on HTC EVO 3D
There are lots of places online to find 3D content to watch on your new HTC EVO 3D, but since some videos are in anaglyph 3D (the type that requires red and blue glasses) and watching Flash videos in the browser isn't always ideal, your best bet is to stick with the preloaded YouTube app.
Some of the user-generated content is amazing, the videos are free, and all the 3D vids are easily identifiable thanks to a little 3D badge that appears next to them.
There's obviously much more 2D content out there than 3D right now, so don't waste your time doing general searches hoping to spot a 3D icon next to one of the videos. Instead, do a search for "3d" or "yt3d" (YouTube's 3D tag); you may not find the kinds of videos that you'd normally watch on YouTube, but at least you'll put that parallax barrier to good use.