As far as making the bench(es) "pretty," I've considered using "found" objects (i.e. chunks of Montevallo bricks, rusted metal o-rings, bottlecaps, etc.) and, of course, the leaf imprint method that our professor suggested is also a very cool idea. Implementing colored concrete might be cool. I haven't researched how it works yet, but maybe it could be used to accentuate the leaf imprints (or whatever) rather than make the entire bench a solid color.
Cool concrete benches I found, some of which are are in no way practical for us to make/use at Hill House but I thought were cool, and others that look simple and do-able: