Always clean acrylic with acrylic cleaner -- never glass cleaner. I like Novus #1, but there are several good brands on the market, which will not only clean the acrylic, but leave a temporary anti-static property, too.
Apply the cleaner sparingly; applying it to the cloth, and not the surface, is a good suggestion. Buff thoroughly to remove all streaks. And use a soft, cotton cloth (I prefer to use a 'real' diaper).
The 3M synthetic cloth made for glass cleaning is good, too, but watch out for the hemmed edges, as their stitching will scratch.
(Shameless plug, FYI: Cleaning, scratch removal, handling, and cutting will be part of the new "Understanding Acrylic Glazing" class at WCAF, Tuesday, 1/25/05, 6-8 pm)