What can I do to make figures I've created generally available so others can use them? I have spend over a day making beautiful figures in Tikz
for project proposal seminar.

The figure are beautiful (the code is not).

These figures are to an extent reusable,
since they are about existing well known methods.
I didn't use the diagrams from the papers as I wanted to take advantage of the extra space I had on a slide, rather than the narrow 1 column images from papers. Also because I didn't want to try and cut any images out of the paper PDFs, since I would lose the vector scalability.

What can I do, to make these images generally available so that others can use them? (Benefit the community by saving others time)

Further more, when I publish my own work with figures, what should I do with the figures to make them available? Should I perhaps on my website with papers, include a .zip of the paper source and images?
You can 


License them under a Creative Commons license that allows reuse. Put the figures with a notice regarding the license terms on your own website.
Contribute them to Wikimedia Commons. If appropriate, you might also add them to the Wikipedia articles for the methods they are about.
Post them on a site like Figshare which gives them a DOI, to make it easier for others to cite them when they use them.
If you're willing, also make the source code available under a permissive license (with whatever disclaimers you want to put about the code not being so beautiful...) so that others can create modified versions more easily. (You can put code on Figshare, too.)