Why aren't there voting alternatives?
 

For example.. runoff voting, which allows one to "rank" the candidates, or approval votin, which allows a voter to vote for more than one person.

These seem like a great idea, so why haven't they been implemented?

What immediate cons would there be to allow someone to vote for more than one person?

I have to get ready for class, so you're gonna get the short answer for now:

Elected officials are the ones who make the rules for voting. We primarily elect officials from two parties who prefer power over what may be right. They recognize they may LOSE some power by allowing such a change. As such, they do not change the rules. They will not change the rules until they are threatened with losing votes. Hence, I don't vote for them.

One reason could be that the person with the most third place votes, but no first place votes could win. A strong Kerry voter would put Kerry first and then just fill in his neighbors. If you really want Kerry to win, you wouldn't even put in the Libertarian or other third party candidates for fear that might have an impact. Same with the Bush people. If you really wanted a third party candidate to win, you wouldn't put Bush or Kerry anywhere on your list. Then again, a lot of reasonable people would simply rank their favorites and let the chips fall. My guess is that most people would still just make one real vote under that system.

And, oh yeah, the dems and reps would never approve. And if another party got powerful enough to effect such a change, it would probably cease to be for it.

That pretty much sums it up, right there.

There are voting methods, such as approval voting, which eliminate this possibility.

http://www.electionmethods.org/
http://electorama.com/

I don't think this to be true at all. Such a change at this point is an intrinsic part of most third party platforms. If the Green or Libertarian Party were to gain power and not actively seek such reforms, they KNOW they will lose most of the people who voted them in in the first place. Furthermore, unlike the Republican and Democratic parties, the Green and Libertarian Parties tend to be more ideologicaly pure. This helps to prevent elected officials for either party from supporting what benefits them as opposed to what fits into the party's greatest ideals.