I spent today extracting functionality from populus into three new python libraries. All of these have been extremely useful in my contract development and I hope they can help others now that they can be used independently of populus.
I would be remiss to not mention the pyethereum library by Vitalik as well as the eth-testrpc library from Consensus. The ethereum-abi-utils library borrows heavily from the internals of pyethereum and ethereum-tester-client similarly borrows from the internals of eth-testrpc. Thanks to the authors of these libraries for letting me stand on their shoulders.
Provides an interface for Ethereum contracts as a python object.
Ethereum ABI Utils
Low level tools for ABI encoding and decoding.
Ethereum Tester Client
This is a drop in replacement for the python RPC or IPC client which interacts with the pyethereum.tester module.