here are a few ideas i came up with:
-structured vest - probably my favorite choice. it's fashionable without looking too trendy, so it'll fit your classic style. if you want to update it even more, try adding a brooch on the vest or even a belt around the midsection of the vest.
-sweater vest - similar to the structured vest, but it has a preppier feel to it. would be nice during the autumn/winter. not sure how preppy you care to be, so this look might not be for you. i could definitely see you pull it off though.
-high-waisted belt - think ana with her fabulous chef blouse. although the standard button-ups lack the architectural details of her blouse, you can still pull off the basic look. it would look great over dark denim.
-bold-colored cami underneath - try it with just the top few buttons open. adding layers of pearls, beads, or chain jewelry would look fabulous with this. also, a bold color for the cami would add a great burst of color
-cardigan or blazer - maybe more of an obvious choice, but blouse always do look great under these. since the button-ups lack any fun details, accessorizing with brooches, necklaces, belts, etc. will again add some more visual interest to the look.
-scarf - a long thin scarf, worn with both ends in the front (not sure exactly how else to describe this style) would look nice. you could also try lariat style, but that might be too bulky over the collar.
