Chrome for standard browsing - fast, easy, nice interface. Simple features like the ability to resize textarea input fields are great for normal use.
Firefox for web development, for the firebug extension alone. Couldn't work without it!
IE for sites which don't work on the above (eg. old company intranet).
Recent versions of FF very slow and memory-hungry, which is why I switched to Chrome for normal browsing and haven't regretted it.
Fair enough to those "what's the point of using anything but IE" users, but for the time it takes to install something else I prefer the question "why settle?"