Do a google search on third party plug-ins for FCP. Only you can determine what “best” is. I use Boris Red, BCC, CGM, CHV, 55mm, Joe’s, and Nattress. Each has its own purpose.
FCP 6 does not offer anything more.
For you, I would suggest Boris Red or BCC from Boris. I think Digital Juice products would be good for you too.
One thing to keep in mind, do not over use filters just because you have them.