Hi David and welcome to the Q&A Forum!
Your best bet is a polarizing filter or a half neutral density filter. A half ND filter is very useful for landscape photography in situations as you describe.
http://www.hoyafilter.com/products/hoya/oef-08.htmlThere are also hybrid filters that combine the effect of two different filters in one ring: ultraviolet and polarizer.
http://www.hoyafilter.com/products/hoya/gf-05.htmlYou can put more than one filter on a lens, but it's not usually recommend if you want the highest quality a lens can deliver.
Here is additional information on filters:
http://www.digicamhelp.com/accessories/filters/