I collect cels because I love anime.  I love the 
art style of the series, the bright colors and 
character designs.  I love to look at anime art, 
whether it's a poster, pencil board, wall scroll, 
art book, dvd, or cel.  
Cels are special because not only do they have 
awesome pictures of my favorite characters, but 
as has been mentioned, they are a piece of the 
anime itself- I look at my $15 cel of Miaka's off 
centered back and feel thrilled because it's part 
of the opening of one of my favorite series.  I 
remember watching the series for the first time, 
and feeling so excited every time I watched the 
intro to a new episode, because I loved the story 
and couldn't wait to get to the next part.
Anime cels are like pictures of your heroes. I 
spend most of my free time (probably too much) 
enjoying art and fantasy stories, and anime cels 
are part of my favorites.