Filter recommendations for a g617

[Jarvman]

I've never shot colour landscapes before, only black and white which means the furthest I've gone as far as filters is slapping a red, yellow or orange on the front of my lens. I'm beginning to shoot colour slides with a recently bought G617 and while some of my early images are looking nice, the sky is either non existant or lacking impact. I know I need to get hold of some graduated ND's, but what would be suggested as well? Also, what filters should I go for? Supposedly Lee filters are the way to go yes? Any advice? Cheers

[freygr]

For Color a polarizing filter. A graduated ND is nice to balance the sky to the foreground.