Meagan Fisher posted a great roundup of flat icons today, including the awesome Glyphish and Icon Sweets packages that I’ve used in multiple projects over the last few years. Highly recommended!
I can’t overstate the value of a good flat, sharp, detailed icon. You can style it any way you please, use it in a variety of projects, and communicate difficult interface concepts in a 16 pixel space. Considering the incredible amount of work that goes into designing each icon, and the quality exhibited below, these sets are scandalously low priced. So get ready to do some serious tax-deductible shopping.