Noise Ninja. A lot of what I shoot requires high ISO's and NN works for me. PhotoKit Sharpener. It's a sharpening workflow, that was developed by some highly respected people in the digital world. And it works.
Both programs have trial versions. I would recommend visiting the respected websites and download the trails to test out yourself. In the case of PK Sharpener, I would read Bruce Fraziers artical about why a sharpening workflow should be considered with digital images.
I do have other plug-ins, but these are the two that I use on a regular basis and like very well.
The destination is our goal but its the journey that educates us. KeithR