A great way to multiply your bitcoins is to invest them into 2nd generation crypto currencies.
There are a lot of new currencies and protocols coming out now that are more technically advanced than bitcoin.
Mastercoin
Next
Counterparty
EMunie
Ethereum
Colored Coins
Zerocoin
I think diversifying between these new currencies is a great way for you to multiply your bitcoins.
But the skill is in picking the winners not the turkeys - not an easy task when there is a new altcoin born every week, and they are getting more and more complex