The top holder of Bitcoins is the unlikely named 1933phfhK3ZgFQNLGSDXvqCn32k2buXY8a with 111,111 units of the crypto-currency (up from 40,000 units in the summer of 2011) for a total value over $110 million. Perhaps most interesting is these 100 Bitcoin holders represent over 20% of the entire outstanding amount of the alternative currency.

The following 100 Holders represent 2.23 million Bitcoins of the 11.12 million total oustanding currently...

(click image for full list)

and the Number 1 Holder has been adding (though hasn't added since Feb 2013...)

And the concentration of Bitcoins has fallen from its early incarnation highs but has been static for recent months...

Source: BitcoinRichList