Since icons are always displayed in 16px, I've only uploaded them in this size but I can provide them in other standard sizes if necessary.
Here are a few choices of icons for each cause. Let's choose from them here and I'll make the pull request in github. Keep in mind that we're trying to keep them consistent. It won't be always possible since some of them are brand icons. All the following icons are either from the tango icon set which is the one already used by Jenkins, from the original brand/project or from different sets of icons found in iconfinder.
In terms of licenses, most of them are under CC Attribution 3.0, others are under The MIT License or Free Art License 1.3. The Tango icon set is in the public domain.
I've ordered them by preference (IMO).