I find Liquid Instruments very useful for adding quick guitars/sax/vocal bits to my tracks. The best thing is the auto tempo and scale adjusment when Im auditioning the phrases, and then quickly modifying them within the vst (melodyne based) to suit my composition.

Are there more vsts that have instrument phrases that auto match to my song tempo and scale?

I used to use acid libraries, but they dont have the flexibility of liquid instruments and sound distorted when time/pitch stretched. I would have to import them into melodyne and adjust.