Question : Problem: What is the best home monitoring system for temperature, flooding, power outage...

I am looking for a home monitoring system that will let me do the following:
- alert on low temperature
- alert on basement flooding
- alert on power outage
- provide internet access when power is available
- wireless sensors

The alerting on power outage is possible through a POTS line, since this would not require AC power.  A system with a battery backup would have enough power to sense the outage and then send out an alert via telephone.
The internet access would be re-configure the system remotely or view the temperature from the remote sensor.

Is there such a system?

Answer : Problem: What is the best home monitoring system for temperature, flooding, power outage...

Probably the most-widespread is X10 - http://en.wikipedia.org/wiki/X10_(industry_standard)

But I did not find any sites that listed all the types of sensors you want to utilize.
If you have a sump pump, there is likely a set of contacts on its float that will close when it reaches a certain height above its 'on' level, so that could trigger an alarm to warn of imminent flooding.
Sample vendor site - http://www.smarthome.com/solution25.html

There are sensors of every type imaginable for programmable controllers such as the SLC ('slick') 500 series (I think 505 is the latest) made by Allen-Bradley/Rockwell. That's an industrial-strength solution, however, with price tags to match. Not unlike using a Cisco 3825 router to distribute your home internet connection.