Yamaha KX25
I got myself a KX25 somewhere around 2008 for like $25. Guitar Center had discontinued the item and was clearing out inventory.
I never used it for much—25 keys is not a lot—but it was portable and had 4 CC knobs that were very convenient for controlling parameters on the LameStation. As a result, it became a fixture on my electronics workbench and actually got quite a bit of use.
It did send an annoying MIDI heartbeat thing that I had to explicitly program the LameStation to ignore. Haven't had another controller do that, so not sure why this one did.
With the demise of LameStation, I found myself needing this controller less and less and eventually gave it away. Sometimes I regret that, because it was still in excellent condition at the time. Such is life.
Things I've created using this gear: