I like ambiant-mate icons theme but, as for me it lacks apps icons, so I just added some.(firefox, thundrebird, chromium, system-monitor, terminal, sm-player, keepassx, keepasxc). You can write here and ask me to add icons for apps you need and I'll try to find something that fits this theme.
Here is an example how my plank dock looks now with new icons.
P.S. I did not draw any of them, just tweaked a little bit.
UPD: Add some icons from elementary icon theme for mimes, categories, devices, apps and a few other icons from different themes. Control centre now looks more organic.