I have seen many very interesting ways of connecting mathematics with the arts and computer science. In particular, there was a big push in the 80's and 90's with popularizing fractals (an aspect of nonlinear mathematics) and computer science that included mathematical results in some art gallerys and bestseller books. Most of the initial mathematics of fractals can be easily understood by a strong high school student.
With some more difficult mathematics, music is very amenable to mathematical analysis, by looking at fourier analysis of particular songs and comparing the frequency distributions of the songs.
Image analysis, compression and wavelets are some intriguing ways of tying in art with mathematics and computer science.
In all cases, starting with google and any of these search terms will turn up some very interesting links as a starting point for you.