Have you looked at Armory?
From the changelog (Version: 0.88-beta (18 Apr, 2013)):
There is currently a more recent version in testing, which might have better usability. I haven't tried it.
Edit: Ah, you are looking for a brain wallet. Doubt Armory does that. Maybe it is useful anyway.
Thanks From the changelog (Version: 0.88-beta (18 Apr, 2013)):
Quote
Fragmented Backup Scripts (Expert Only). Two new scripts added to “extras” directory: “frag_wallet.py” and “unfrag_wallet.py”. These scripts can be used to split your wallet into pieces/fragments using Shamir’s Secret Sharing. This is only available from the command line, but will be integrated into the application itself in the next release. The new interface will include restoring fragmented backups created with these scripts.
There is currently a more recent version in testing, which might have better usability. I haven't tried it.
Edit: Ah, you are looking for a brain wallet. Doubt Armory does that. Maybe it is useful anyway.
