ZBrush is the industry standart. There are other tools that allow you to do that: Mudbox, 3D Coat....

I personally like 3D Coat. It has a very clean interface, where ZBrush seems to be "arcane" and hard to understand, and very good retopo tools (another thing you might need to do if your high poly sculpt no longer fits your low poly model enough).

3D Coat is also cheaper, about half the price of ZBrush...

Now, you can also use Blender for sculpting. Any 3D Package I know of nowadays has its own sculpting tools. While they might not be as powerful as what you get in ZBrush or 3D Coat, they might do the job without needing an additional tool (and an additional license).

Then there is the option to create the details directly as a normal map in a tool like "nDo", a Photoshop Plugin. If you your object is rather simple, and so are the additional details needed, that might be a quicker process than sculpting the details and baking it back to the low poly mesh.

Thank you for all your advice. I am using Z-Brush to give more detail with my model and I am getting good results so far. I am using videos to help me guide me through Z-Brush since it has been awhile since I used it. Bought it for school so might as well used it.

If I recall correctly, you are supposed to baked the high res model in the lower res to bump the detail.

You need to differ between a hi-poly ZBrush model and an higher poly in-game model. Right, if you want to add baked details, you should go for ZBrush, sculp them in and bake them to a texture. But if you need more polys for the ingame model, you need to remake your current model. Ask your employer what he is missing. Is it the silhouette of the model which is too rough, then you need to remodel your model most likely. Does he want more details, e.g. single fingers should be animated separately ? Or does he want more surface details, then you should go for the zbrush/bake approach.

I general make the models look more high tech. I know that just putting more details (higher textures) can make model looks more high res than it actually is. Your first example is what I planned to do for all the models while making a higher poly model for those I think needs it. For the record, this is for demonstration, not an active game, yet.