Do yourself a favour bro and spend the $100 and get an 030 for your a1200 and open up a whole world of awesome demos. That being said there are a few that will work on stock machine. Check out pouet.net (think thats the name) or the ADA amiga demo database
Actually my REAL Amiga has an 030/50MHz board, I am trying to get stuff to run on UAE on my Mac, I haven't figured out how to emulate an accelerator board on it yet...