Back to architecture, shall we? I usually go with what I call the 7-1 pattern: 7 folders, 1 file. Basically, you have all your partials stuffed into 7 different folders, and a single file at the root level (usually named main.scss) which imports them all to be compiled into a CSS stylesheet.
base/ - resets and basic typography
components/ (or blocks/) - components with their separate mixins, images, variables, (also possibly scripts and markup)
layout/ - structural styling for main elements (asides, mains, headers etc.)
pages/ - styles specific to certain pages
themes/ - if site contains several color/typography themes - put here styling that should vary according to different themes
abstracts/ - common vars, functions, mixins, extends
vendors/ - external scripts or frameworks specific styling (jq-ui etc.)