I use a Yamaha P85 piano as a controller for my PSR-S900 and also as a stand alone instrument.

It has a lovely 88 key weighted graded hammer action, MIDI ports and is very lightweight at 25 lbs.

It lacks pitch and mod wheels, which may or may not be important to you.

It is also relatively inexpensive.

Ian
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Yamaha Tyros4, Yamaha MS-60S Powered Monitors(2), Yamaha CS-01, Yamaha TQ-5, Yamaha PSR-S775.