There are alot of 3D engines out there for you use but you need to define the question a little more.
For example,
What type of engine are you looking for? such as indoor or outdoor engine?
That makes a big difference in your search because most free engines will either offer one or the other.
What type of model support do you need? 3DS, OBJ, .X etc…
What graphics API pipeline are you or your coding team most comfortable with? DirectX, OPENGL, GLIDE etc…
What programming language should it support? VB, C, C++, JAVA
Does the engine have to support Animation? if so how?
etc, etc…
But to help you on your search here is one that I have been looking at its called ORGE and it seems promising.
To be honest I have been considering building my own if I could find the time…but Im still considering it.
Good luck on your search.