Coin certification is a subject that has strong advocates for and against.
Most agree on the four top services:
NGC
PCGS
ANACS
IGC
To often collectors use the grading services as a crutch. Grading, while an art form, can be learned by anyone willing to put forth the effort.
So when should you slab your raw coin?
Key dates in any series, and coins that are often targets of counterfeiters.
Remember, buy the coin, never the holder