RealGuitar, RealStrat, RealLPC, Ivory II Grands, Melodyne Assistant, Vienna Symphonic Library, EastWest Hollywood Strings, EastWest Fab Four, Vir2 Acoustic Legends HD, Vir2 Electr6ty, Guitar Rig 4 Pro. I also have AAS Strum Acoustic Sessions but I never use it.
I also use the Fantom synthesizer that came built into the V-Studio 700. It is harware but is used as a plug-in.
I don't know if you want to count these but I use several of the things packaged with X1 Producer: Session Drummer 3, SI-Electric Piano, and SI-Bass. I have looked at Dimension Pro but have not needed it so far.
I have WaveLore's steel guitar for Kontakt but haven't had a chance to get into it. I have used external synths for this sound so far.
EDIT: Just realized you asked for recommendations: Out of all this, I could not live without Ivory or RealGuitar.
For orchestra, Vienna is way more efficient and easier to use than Hollywood (plus it has the whole orchestra) but since VSL no longer sells the same special edition packages as before, I am not sure what it would cost to get everything you need.