Coin Collecting 

Investing in coins is one of the great reasons folks get into coin collecting in the first place.  I know thats how it was for me.  It wasn't long after discovering certain modern year silver eagle coins were worth much more than other years, that I got very excited about collecting coins as a hobby and an investment.
I once thought that diversification with a majority in precious metals was the key, but now I don't think that way.  Think about it, what would be more valuable over the long term?  Gold bars, or the equivalent in gold coins?  Any collector will tell you to go for the coins instead.  They not only offer the daily spot price value of the precious metal, they also offer the premium associated with the coin itself.  If it also happens to be a year that less of them were made, its likely to be even more valuable.
With the exception of a precious metal price itself dropping in a huge way, you can't really lose if you invest in coins instead of bullion or bars.  And even if there were a huge price drop you would still have the premiums attached to coins which bullion doesn't have. You  generally stand to gain a lot more over the long term if you invest in coins rather than metals themselves.