Civ3 isn't really graphics intensive, so you luck out in that department. The largest maps run smooth as butter on this comp, which only has a 128 MB card(a Radeon 9800). Anything probably from a Radeon 9500 or newer will do. I would recommend something from the ati radeon series, but like i said, most anything will do. Best priced depends on how cheap you feel like going.
You'll need a seperate sound card. My personal recommendation(based on price/performance/reliability) would be ANYTHING from the soundblaster series from the past year and a half.