New to me... I just discovered "Open" acrylics from Golden Paints. This is an acrylic that dries like an oil allowing blending with acrylics. Takes a couple of days to harden/dry. If you want it to dry faster you just mix in some standard acrylic paint. Golden has a whole video library showing how their acrylic paint and glazes work. It is a kind of mini-tutorial on acrylic paints AND techniques.
http://www.goldenpaints.com/VIDEO/library.php
Ken
The Virtual Paint Mixer application here on the same website looks to be very handy: http://www.goldenpaints.com/products/mixer/
dave