Any remote that can control earlier TV3... unless you're looking for touch pad and game controlling functionality. For that, you'll have to be patient to see if third parties like Logitech or Universal Remote Control, Inc decide to make one with greater compatibility with the TV4 remote.
I use a Harmony in addition to the AppleTV 4 remote. The issue with the Harmony (and I suppose most/all of those remotes with directional buttons vs trackpad) is that scrolling long distances is a pain.
Two articles from Apple that may help. I have a Samsung TV, and if I turn on HDMI-CEC I can use the remote that came with the TV to control the Apple TV. The second article suggests that you can use (most) other remotes if you teach the Apple TV how to work with them.