Here are some large images which could be used as posters. Click
the thumbnails for larger versions.
Posters related to the Hopf fibration
Fibers showing the 12 cores for rings of dodecahedra making up
the 120-cell. The view shown here is looking
straight down the z-axis. I don't have a poster-size version
of this one, so you'll have to use the
Sage source to output a high-resolution version.
The periodic table of finite simple groups, by Ivan Andrus; he
announced and explained it on
this blog post
This is a very large image (256 Megapixels = .25 Gigapixels; file
is 17MB). It's a fractal arising from iterating powers of the
complex cosine -- different colors indicate different amounts of
periodicity. It's an open question whether the coral-colored
region in the middle ("period 1") is precisely a cardioid. I
wrote about it on
a mathoverflow question which has some partial answers, but
I would really like to know more about it!
This calendar from 1988 is one from the early days of
computer-generated math pictures, and shows 12 minimal surfaces.
Unfortunately I don't have any higher resolution than this, and
I've lost or forgotten the original source.
The info pages from the 1988 calendar!