libcrypto++, version 5.6.2 or greater (i.e. with SHA3 support). Because it's so recent, it expects this to be built in a directory libcrypto562 in the same path as cpp-ethereum.
A decent C++11 compiler (I use GNU GCC 4.8.1) and a recent version of Boost (I use version 1.53) and leveldb (I use version 1.9.0).
Do *NOT* use an editor that automatically reformats whitespace away from astylerc or the formating guidelines as describled in CodingStandards.txt. Your contributions will be refused and your commits will be reversed.