The first swap I participated in was seasonal-themed. Colours came out a bit wonky in this picture but here they are for the record:

To see what ATCs look like when a real artist tackles them, have a browse at Joumana Medlej's ATC gallery. (Seriously, you want to go and look.)
Last night I went to a gallery show by a co-worker of mine who's leaving the country in a few weeks. All of her photography, paintings, and 3-D collage boxes were available for donations and I was lucky enough to get some beautiful pieces of wall art and photographic prints, including this one:
Her RedBubble page is here and I'm sure she'd be happy if you went by for a browse.