I rather like the idea of grouping Bitcoin units by 10,000 as others have said.

It fits in well with Bitcoin's design of 8 decimal places in total.

Grouping by 4 decimal places makes sense here, because 8 decimal places fits cleanly into two groups of 4.

Japanese culture already uses grouping by 4 decimal places: man, oku, chou, kei.  (Maybe this is why Satoshi chose to divide Bitcoin into 8 decimal places, and not 6 or 9, as a Western designer might have done?)

Chinese culture also groups by 4, and we all know how important China is to Bitcoin.

And, we already have a unit for 10,000 BTC, the Pizza (named after the first successful real-world transaction), so this is a smooth progression of units.

10,000 Satoshi = 1 ?

10,000 ? = 1 BTC

10,000 BTC = 1 Pizza

OK, enough rambling, here are my nominations for the "?" unit:

Nakamoto (goes with Satoshi)

Finney (memorable, and a tribute)

Others have already mentioned these, but I agree with them.

Josh