Here are some great links to read, thanks to a benevolent benefactor!
whats everyone doing for health insurance
trying to figure out the health insurance maze
a useful health insurance information website
need medical insurance recommendations
The insurance website in #3 could prove most useful.
Useful national coverage doesn't really exist. Policies are written or offered on state by state basis.
WHERE you claim residence matters, because insurance companies' policies VARY in each state.
Look closely at the travel/instate restrictions for each new company you consider.
One of the primary reasons to keep your policy with a MAJOR vendor is the negotiated fees for tests and procedures and emergency room visits, etc.