"Modeling" with regard to miniatures encompasses the building, modification, and detailing of miniatures, and it is a key part of building an army for me. Modeling is how I attempt to convey details (or mystery) about the forces I use and the character of those forces. Modeling is how you make your army stand out from others.
An early source of modeling inspiration for me were two White Dwarf articles: one about Dave Taylor's Adeptus Mechanicus army (back in 3rd edition, before there was such a thing, or models for them) and one about his Adeptus Custodes army (also back in 3rd edition, before there was such a thing or models for them). The creativity that went into kitbashing each model to not only represent the unit it was actually using rules for but making the units look different and feel right for the rest of the army still inspires me. Pictures below, and a link to Dave's blog.
Adeptus Mechanicus tank (I believe this counted as a Leman Russ).
Custodes (I believe these counted as Grey Knights at the time).