The following web pages have excellent information about using SU-8 for
microfluidic devices.  It is easily spun on and patterned using UV
light.  A multi-level process has been developed to form microchannels.

http://dmtwww.epfl.ch/ims/micsys/subtopics/projects/su8/EPON.html
http://dmtwww.epfl.ch/~mheuschk/