The caveat to what @MilesT said is that standard Roku IR remotes won't work on a Roku TV. There are different code sets for different manufacturers. If it's not a Roku TV, but a TV with a Roku attached, then any universal remote that supported Roku (it will say if it does) will work, as he indicated. The Roku TVs are a different beast though.
DBDukes Roku Community Streaming Expert Note: I am not a Roku employee.
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Agreed. I'm constantly dropping it. And the volume/mute buttons are on the side, so even gripping the remote causes the sound to adjust. It probably costs only pennies to manufacture but I'd pay more for something a little more substantial.