After the my last post, it appears that you appreciate any pointers to further icon resources, so I thought I'd share some more info with you.
You can find a plethora of icons - even free ones - all over the internet. The only thing that you need to make sure of is the correct attribution or license use, but usually that's not much of an issue.
Hongkiat compiled a whole bunch of icon sets for varying use, which you can find on their blog. A lot of them try to imitate the 3D look of the past decades, however, there are quite a lot of 2D, modern style icons that you can easily use in your apps.
Another really great site - and I can't repeat this often enough - is The Noun Project. Here you find many icons of different styles and variations for your convenience. They come as vector images, too, so you can scale them easily to fit all your apps' tile sizes. Each icon has their own license though, so make sure you check the conditions before using them.
Last but not least: Icon Monstr. Lots of free, modern style icons.
Feel free to leave more (free) icon resources that you find valuable in the comments :)
I would kindly suggest www.syncfusion.com/.../metrostudio
which is one of the best applications I've ever seen for Metro icons ! <3
You should also check http://www.iconspedia.com, they have thousands of icons