"At the moment it is in to create simple but elegant designs. A good example is the metro design used by Microsoft in numerous products. Of course you need to find a fitting icon first so here is something I want to recommend to you because they are for free and you can use it in commercial products as well.
Some of these I've seen or mentioned, but some I haven't... (and new, free graphic sets makes me smile... :)
Related Past Post XRef:
300 Windows Phone 7 Icons, Creative Commons (with *.XAML, *.Design and *.PNG)
Windows Phone 7 Icons.. Before you search the web, check your hard drive
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The Noun Project, XAML’ified… or The Noun Project converted for you to XAML and PNG’s
“The Noun Project” + SVG + Free + Metro like look and feel + 500 = Happy Windows Phone 7 Developers