Health insurance that covers pre-existing conditions

We should reframe and clarify the question first in order to provide a more useful the response. Otherwise the response might not be useful. For example, if you are continuing coverage with the same insurer then all health insurance plans will cover pre-existing medical conditions. If you don't have prior coverage and are asking which insurance will immediately cover the costs of an expected upcoming expense, then none of the available health insurance plans will do this. If you enroll in a new plan and keep it long enough, most of the health plans available will eventually cover pre-existing conditions. Of course, these responses don't help much with your decision-making.

What you are more likely asking us is "what health insurance provides the most liberal coverage for pre-existing medical conditions with the shortest waiting period if I have no prior coverage?".  Framed this way, the question is easier to address with a specific recommendation.

Core Health Insurance plans underwritten by United States Fire Insurance Company provides the most liberal coverage with the shortest waiting periods for most people. There are currently 8 different Core Health Insurance plans to choose from. These range from inexpensive to pricey, minimal benefits to rich benefits. All are limited benefit insurance plans which means that the policy states the maximum coverage the policy will provide. Some outpatient and doctor visit benefits for pre-existing medical conditions are available immediately when the policy starts but the more costly surgical and hospitalization are available in six months after the start of the policy. 

Much additional information is available online at http://www.freedombenefits.net/affordable-health-insurance/Core-Health-Insurance.html