You can’t go wrong with Font Awesome

Font Awesome gives you scalable vector icons that can instantly be customized — size, color, drop shadow, and anything that can be done with the power of CSS.

Web UI icon embellishments are very popular in modern design. Traditionally the icons are packed into one raster image and the appropriate glyph is extracted through clipping. This works well but has some drawbacks: suboptimal for scaling, and potentially tricky in aligning the height with neighbouring text.

Embeddable fonts provides a more powerful alternative – package the icons as font glyphs! With this technique comes all the benefits of fonts: consistent heights & widths, vector scaling, easy colouring & styling, etc.

A cool Open Source GPL package to start with is definitely Font Awesome. It has many icons and out-of-the-box CSS styles ready for use. Check it out.