So, I recently picked up Native Instruments Free bundle which included three synths and guitar rig 5 cut down version.
Are there any other virtual instruments of effects plugins out there that have an operational cut-down version that you can download and use?

If you buy a digital copy of Computer Music magazine, they have a bunch of (very good) cut down versions of commercial plugins.  There's a great cut down version of U-he's Bazille in this month's edition.  
 
You can buy an issue through Zinio or perhaps Google Play or whatever Apple uses.  
 
It's definitely worth the $5 or so to get access to all those great plugins

Here's a link for Zinio:  https://www.zinio.com/www/browse/product.jsp?rf=sch&productId=500258045#/
 
Once you download the issue, you go to the site below, register, and then answer a couple of questions about the issue to get access to the goodies.
 
http://vault.computermusic.co.uk/login/
 

I tried to put links for you in a separate post, but the forum software took them away.  (eyeroll)
 

Smokey's suggestion is right on the money. Just one (digital) copy of CM and you'll get access to the CM Vault full of classy cut-down freebies.

Agree with Smokey too.
Also try ikmultimedia. They have sampletank free and a few plugins free. Check out musicradar.com. They had just recently posted an article on best free plugins.

You can also go here for plethora of freebies...

http://www.vst4free.com/

You can just go to a web site of a company you like or have heard about and look for the freebies. Almost everybody has some. Get RoughRider comp from Audio Damage. I still reach for it often. PSP PianoVerb is a good one.  Groove3 has a video tutorial called "Mixing With Free Plugins" by Russ Hughes, IIRC.

I have tried u-He Zebralette, a cut down version of u-He Zebra2, and think it sounds really good. It also has a user guide in the zip file.  Demo of Zebra2 is included.
http://www.u-he.com/cms/zebralette
 
"OK, Zebralette is just one of Zebra2's oscillators packed into a simple, easy-to-learn framework – but you have everything you need to make some pretty amazing sounds. Sounds that can be directly loaded into Zebra2 later. And should you eventually decide to upgrade to Zebra2, you will already know everything there is to know about the oscillators – which is quite an advantage!

Zebralette has two LFOs (one per voice, one global), a multi-stage envelope and three on-board effects (chorus, EQ, delay). Not forgetting Zebra2's famous dual spectral effects, which include several squelchy filter algorithms.

Megasaw? Zebralette also goes to eleven.

So: Because the Zebra2 oscillators are so powerful, Zebralette is actually a great little synth in its own right, and it has the same pristine audio quality as the mighty Zebra2... try out the new presets and see for yourself!"
 
Here are some tracks composed exclusively with Zebralette sounds for the "One Synth Challenge":
https://sites.google.com/site/kvrosc/osc-32

U-he Zebralette
Indiginus Analog Orchestra Lite
Bolder Sounds Music Maker
Universal Sampling Euphoria demo (don't know if this is still available)