Interactive Map of USA with pop ups

We're looking for someone to develop a web graphic which would be a somewhat interactive map of the USA. We want to plot on the map every city that's over 400,000 people in population, then we want you to be able to mouse over ths city and a message pops up saying "Denver - Under Contract", We need to be able to change the terms for each city easily, another city might say "St. Louis - Available". We also want to be able to change the background of the map to include colored circles on the map and we'll change that image as we expand to new cities. Not sure the best platform to build this on.