I know this is really, really specialised, but I'd thought I'd share it....
At the moment I am going through a "Flat" phase and these icons look great on my phone. There are over 2000 icons, so that can't be bad :)
He has 8 packs at half price, https://play.google.com/store/apps/developer?id=Vertumus&hl=en,
but this is my favourite.