LogFAQs > #940436526

Get rid of First Past the Post voting for a system with ranked choice or even just "pick as many as you want, highest vote total wins". Without having to choose (only) the lesser evil, suddenly you can cast a vote for 3rd parties w/o throwing your vote away.
That's the root problem that's lead to two party politics (though the ridiculously corrupt corporate campaign funding and consolidation of major media under a small group of wealthy people also are major causes), striking it down helps everything else improve.

But yeah, out of that list easily the electoral system. Even if 3rd parties were viable, electors could just ignore the will of the voters anyway, plus it's outrageous how much more valuable the votes of one state are vs. another (and the fact that only like 12 "battleground" states actually matter at all)