I prefer using oxides to glazes on my pieces, one reason being the subtle “watercolor” effect you can get on the clay surface when using them.   A great resource about oxides:

http://www.bigceramicstore.com/blog/top-10-ways-to-decorate-with-oxides/

I have invested a lot in Mason stains, and combining them is really an experimental process (try alittle avocado or butternut to any of them and you really get a different effect).  Here’s the chart:

http://www.masoncolor.com/ceramic_stains.asp

I found some good info on using underglazes, slips and stains on both bisqueware vs greenware:

http://pottery.about.com/od/slipsengobes/tp/when_underglaze.ht

Also, a good clip about Amaco underglazes, see the lovely surface of their ‘velvet’ line & chalk sticks:
http://youtu.be/-kxTtApM1FE