I recommend checking out
http://organofcorti.blogspot.com/Latest statistics:
http://organofcorti.blogspot.com/2015/06/june-14th-2015-block-maker-statistics.htmlThe ones he's got labeled unknown are in the 'Unknown recurring generation address' table.
1CdJi2xRTXJF6CEJqNHYyQDNEcM3X7fUhD is possibly 21, Inc. Several services have begun labeling as such, and organofcorti mention of that at the top of this week's statistics. There's no hard evidence that it is 21, Inc. and he welcomes input on that.
A comment points out:
1BwZeHJo7b7M2op7VDfYnsmcpXsUYEcVHm is BTC Nuggets, as correlated to their block stats page.
1NY15MK947MLzmPUa2gL7UgyR8prLh2xfu and 1Ar2gRkt1u6k4PToeeTKm1KGmtR2GRA1wL may be related, but unknown.
1GcF7j3YH8Qs8hvNEe7zbrQZftMU6sRLfu seems to have some transaction connections to F2Pool, but that's a weak link.
1Fdpys8g2Dsnk2vyLARdDidAebCafrH2Wb and 1qtKetXKgqa7j1KrB19HbvfRiNUncmakk - no idea, but then they have 1 block each in a week, so that's not very many.
There's several more not listed there that would be under 'Unknown' in his main table, but it's a sub-1% remainder.