Try Fisherfinest Premium microscope slides, very clean for good sections.

Our diagnostic laborabory swears by these, for blood smears, which
require very clean slides.  There is an equivalent slide avaiable
through VWR.  Both are made by Erie, but very clean.  We used to use Clay
Adams Gold Seal slides (also made by Erie) but more expensive.  The
premium slides were a more cost effective slide for same results.

Caveat!  I have NEVER found the perfect slide without cleaning them myself! 
Even the above slides can be funky at times!
Gayle Callis