Can anyone recommend a C++ std::map replacement container?

Maps are great to get things done easily, but they are memory hogs and suffer from caching issues. And when you have a map in a critical loop that can be bad. So I was wondering if anyone can recommend another container that has the same API but uses lets say a vector or hash implementation instead of a tree implementation. My goal here is to swap the containers and not have to rewrite all the user code that relies on the map. Update: performance wise the best solution would be a tested map facade on a std::vector