here is a beta of BetterSnapTool that supports Yosemite’s dark-theme:
It can be used without limitation until 10/10/2014, but only on OS X Yosemite betas.
Please report any issue you encounter!
//update: fixed a few issues in beta2. If BetterSnapTool doesn’t resize properly on your system, please try to unplug and reconnect all external monitors and/or restart your system once.