I usually try to find some good Cote Du Rhone (pretty big, crowd pleasing red) on hand for non-wine drinkers that are needed last minute.

Good ones can be had for $15-20, but of course i'm keeping an eye out on close outs, and buy a case or two.. so normally I get them for $8-10 a bottle.. tasty, easy to please, and not expensive.

(as a reference, I keep about 150 bottles at home in a wine fridge, and a few hundred in an offsite storage.. so it's not a HUGE cellar, but I wouldn't need to go to a store if a dinner invite came up either)..