Check out this set of almost-flat social free icons designed by Sylvain Guizard of PEPSized.com There are 90 different services represented, optimized to 15 different sizes. Each icon has a subtle gradient and border, lifting it off the page, without losing the underlying flat aesthetic. The free icons are provided as a .png and .psd, with named layers for all vectors in the PSD. The icons are free for personal and commercial use.