I use a Yamaha PRS series (one of the older models)
It works well for my needs.

I mostly use it as a midi controller, but it will also accept MIDI output and work as a hardware synth if you want to use it that way. My patches are not arranged in GM order, so if I wanted to use it that way I'd need to create a patch map. SOme models may have a GM set of patches, which would be highly desirable for using it with BIAB... you may want to see if any of the models you're looking at have GM

If using as a controller, desirable things to look for are:
-velocity sensitive keys, (adds midi data that will be useful later)
-pitch bend wheel (helps to make certain patches sound more realistic)


If you wait until February, Craigs list will probably be full of such keyboards that were given as Christmas presents but didn't get touched by kids who preferred to spend all their time on video games