I have downloaded and tested many of them.
For me the best twoi were Neat Image and Noise Ninja. I ended up with Neat image becuase it seemed to be the most intutive for me. In other words, it did a very good job, the controls gave me a wide range of ways to reduce noise and sharpen and finally using it became second nature to me almost immediately.
My second choice was Noise Ninja. It seemd more powerful, but not as user friendly for ME---- others would probably like it and hate Neat Image.
The free trials don't cost anything--- I'd download them and play with them.
Good Luck,
Rolando