There are some lovely ones at Coffeeshop Blog (I think that's what it's called). Google it, anyway. They're free, and worth a look. I used a few of them a lot, then started looking at how they worked and tried to emulate them myself...learned a lot more about how different things work by doing that that just using the plug-ins blind.
If were talking about little plug-ins such as something that sharpens for you etc etc, that is something you should absolutely learn to do without a plug-in.
If were are talking about a commercial plug-in that is a representative of a stand alone program such as Noise Ninja etc, then these are a great way to incorporate a valuable tool into CS or your particular software or compatible version.
Don't get me wrong, there are some neat gizmo, gimmick plugs that are neat-o, but for basic stuff, don't attempt to sidestep learning how to do them yourself where in the end you will learn about and have greater control.