Is There a Distro that is debian, red hat, ubuntu, and mandrive based? I guess what I mean is,
Is there a distro with a super huge package list?

There is the smart package manager, but it still does not recommend trying to mix repositories with differing package formats:
http://en.wikipedia.org/wiki/Smart_Package_Manager

Debian has 18k+, not enough?

Can use alien to convert rpms, pkgs, and tgzs to debs
http://en.wikipedia.org/wiki/Alien_%28software%29

First, there is a tool - alien, and there is an RPM package of dpkg and .deb of rpm. I mean that you can install packages from one flavour of system on a system of another one.

The problem is that if you use different package management systems, their databases will be independent (I am pretty sure there is no distribution that solves that without converting all packages to one format) and some files will be overwritten by very similar, but different versions without (sometimes) even a warning.

If you convert packages with "alien", on the other way, you will have slight dependency mismatches for some exotic packages. RPMs for RedHat and Mandriva are in the same format, and they have the same dependency descriptions, but they may be incompatible due to small version mismatches.

Now it should be clear that the super huge package list would probably be composed of packages with missing dependencies and a lot of package conflicts. So it would be unusable.

Now, please answer what do you want. If you want a few concrete packages, use whatever distribution you come across and alien. If you want automatic dependency-aware installation with packages from different distributions, package conflicts will kill you. If you want some rare software, take a distribution where you can easily (!) create your own packages. Neither .deb nor .rpm formats are exactly convenient for it.

The distribution with the largest package list in their repository is Debian.

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Steve Stites