Motu makes Electric Keys -- a library of virtual electric pianos and such.
I just ordered ten Tyrannosaurus Mouse plates from Amplates.
Samplitude has an interview with John Vestman about mastering with stems. Our mastering engineer, Alan Douches of West Westside Music just hates mastering from stems. I have to say I agree with him. It's better to get the mix to not suck before you go to mastering. Ooh. Wait. That was a really catty thing for me to say.