After years of putting off getting the full version of Kontakt, I finally got it after they offered their recent discount.  Now while the numerous instruments are on sale for the holidays (or at least this week), I was curious what peoples favorites may be.  I have Alicia Keys, Strum Acoustic ( that I see that they updated but don't offer an upgrade -- I read the post) and Rickenbacker Bass, all of which I love.  I'll be spending a lot of time exploring all of the items that come with the full Kontakt, but also wondering what is out there that people really like.
 

It might be easier to answer what is NOT liked for Kontakt.
 
For me nothing. I have 10 Ultimate and a gazillion 3rd party libs. Love them all.
 
 

What bapu said...10 Ultimate is an amazing toolkit. 
 
As for 3rd party libraries: I'm a serious Albion One advocate. Easily my favorite library among all that I own (Kontakt or otherwise). Its the first one I load up with every session. 

Just for starters check out.
Orange Tree Samples Evolution guitars.
Hollow Sun for vintage keyboards and off the wall synths and sound design.

Also
Hideaway Studio for vintage synth and sound design.
Sonic Couture
Sampletekk for pianos.
Rhythmic Robot, Sample Magic, and Tronsonic for some lesser known vintage synths.

I have also been having fun with Session Horns.

Since you listed Strum Acoustic and the Rick Bass, I'll assume you're not a guitar player. If you're a keyboard player who wants to add guitars to your creations, let me suggest some guitars...
 
First, check out the Indiginus catalog. They hit the sweet spot at the intersection of inexpensive and useful. I like and use them all, but my favorites are Renegade and Delta Blues for leads and AGC for rhythm. Also, Solid State Symphony is particularly fun and satisfying for on-the-fly orchestration.
 
Orange Tree Samples offers similar products at the higher end of the spectrum, more full-featured and versatile but at a higher price. Top of that list is my go-to bass, the Rickenbacker, but you've already got one of those so that would be redundant. Second-favorite OTS product is Evolution Strawberry, my go-to for more aggressive lead guitars. But I've not been disappointed by any of my OTS purchases.
 
Falling in between Indiginus and OTS would be Ilyia Efimov. More expensive than Indiginus but less than OTS, more feature-rich than Indiginus but not as versatile as OTS. His nylon and steel-string acoustic guitars are quite good, and currently on sale for $63 each.

bitflipper
Orange Tree Samples offers similar products at the higher end of the spectrum, more full-featured and versatile but at a higher price. Top of that list is my go-to bass, the Rickenbacker, but you've already got one of those so that would be redundant. 
 

Gotta disagree Dave. I own both and they are very different IMO. Warmer (fingered) and vs. clackier (picked).

No doubt, the OTS Rick is the best I've heard. Granted, I may be foolish to argue with a bass player about sampled basses, but I still think nobody (except perhaps compulsive collectors) needs two of 'em. Ricks, that is, not basses.
 

thanks bitflipper... very good advice.  Altho I play some guitar on my recordings if I can, you can't beat the tight, clean output of a decent midi backing guitar. I usually run it thru an amp prog like Amplitube anyway to give it improved sound.  I bought the Delta Blues inst for a country song I'm working on and it sounds nice.  Now I'm on the fence about the AGC or StrumMaker IV for a rhythm/acoustic.  I've had good luck also with the AAS Strum GS-2 for smoe simple country backing strumming.  
Appreciate the advice from the other posters also!

The ones I like come from:
AIR, BigFish, Cinesamples, 8Dio, Embertone, GForce, GospelMusicians, Heavyocity, ISW, NI, OrangeTree, Output, Pettinhouse, ProductionVoices, Realivox, Sampletekk, Soniccouture, SoundIron, Spitfire, SugarBytes, Wavesfactory and Zero-G.
Best ones to my eyes and ears?
Embertone Intimate Strings bundle, GospelMusicians Neo-Soul, ImpactSoundworks Pearl Grand and Ventus Shakuhachi, OrangeTree acoustic guitars, Output Exhale, Realivox Ladies and Blue, Spitfire Albion One, Wavesfactory Mercury Grand.