Recently, I had given reply to the similar query. Please click the following link:
Your query is about "key employees". Why the employees are important to you? Do they have unique skill set? Do they have high-level of performance or is it that their performance is just above-average but getting people with that specific technology is difficult hence you are calling them as "key employees"?
Some of the suggestions on retention of the key employees are as below:
a) First and foremost, giving them sufficient autonomy. However, autonomy also comes with accountability.
b) Finding a good mentor for them. For this, you need to institute "Formal Mentoring Programme" in your company. Click on the hyperlink to know more about this programme. Please note that this programme is different from buddy programme.
Another important thing is to groom their successor well in advance. Of course this is not part of retention planning but you need to have standby for them.
Last sentence of your post reads how can I retain best employees(talent) in a non-monetary ways. Well, my dear friend, nothing comes free in this world. You wanted to retain someone "best" and that too without spending anything. Please note that quality comes with premium. Enjoying both sides of the world is possible but only in dreams!
From India, Bangalore