During development programs for Windows Phone 7 I have met quite often with the problem of icons. I’m not a graphic designer and making a decent icon for the program took me too long. The first attempts to look for an icon in the Internet ended in failure. Of course, I was looking for free solutions. The only think, what I have found it was a set of icons provided by Microsoft.
Unfortunately, the number of icons is not too great. So, I continued with searching the web.
I managed to find the page of The Noun Project. This is a database of free icons, that can be used. The site has a search engine and possibility to choose icons on the basis of categories.
For now, I could not find anything better. If you have other sources of icons, please let me know.