Your vote still matters

So for a certain type of person (Idiots), it is common to hear the phrase "it doesn't matter who I vote for", this can be for a few reasons.

The first and most common I think is that "both parties are the same, man" and if you look at where corporate donors an lobbyists are throwing support, then you would not be entirely wrong in thinking that, however you need to remember that most corporations are not really that ideological, and are hoping for support from whoever gets elected, you really want to look at those behind the SuperPACS or the wealthy individual donors, as well as what organizations have endorsed your candidate and historically support the party.

It is pretty easy to see a difference between any of the current Republican candidates and Hillary Clinton, and even more of a difference between them, Hillary, and Bernie Sanders, Trump is something of an outlier as he has stated he would refuse major donations from people like I described, but is himself massively rich and honestly, no reasonable person would think he is a good candidate, or in fact the same as any Democrat option.
Additionally, consider that under a Democrat in the last eight years, we saw the ACA implemented and survive dozens of challenges, marriage equality become the law of the land, and a fairly large list of other stuff, now many of these would not have happened under a Republican president, but another key point is missing, Obama appointed two Supreme Court justices during his terms, we would not have the healthcare laws we do now if a Republican had them, nor would the marriage equality ruling have gone the way it did  either. In the next eight years, you can bet good money that 2-4 justices will retire, and believe me, you don't want the best of the Republican field selecting them even if you have to have the worst Democrat do it instead.
Right now, there are a few candidates literally attacking the 14th amendment and attempting to strip protections from an entire racial group, you can prevent this by voting.

The second reason I see a lot is that "It doesn't matter anyway, the money will select the politician" This can be read either as if a secret cabal of rich people will choose (which is silly, the cabal isn't that secret) or simply as whoever has the most money wins. But that doesn't seem to be true at the presidential level at least, certainly you need a crapton of money, but according to the data I could find, the two major campaigns raised and spent roughly equivalent money in 2012, and this has been true for the last few election cycles, it seems there might be a point of diminishing returns on campaign spending, which is one reason I feel no fear that the Koch brothers support of Scott Walker will get him into office, the other reason is look at him:

yeah, no

The most valid complaint I've seen is that "Unless I am in a swing state, my vote doesn't matter", this is actually pretty close to being true, but like all things it is changing, and kinda rapidly too. Demographics are changing in this country, white people, the Republican base, are declining as a percentage of the population and the Republicans have been doing their damnedest to make themselves unpalatable to the assorted minority groups in the country, and their representation is increasing, soon states that were off the board will become legitimate battlegrounds, heck according to data I found here, Florida may not even qualify as a swing state in 2016.

And that leaves aside a wildcard in this election: Donald Trump, he has amazing support from the Republican base and a chunk of the more racist independents, but this comes at the cost of basically everyone else with a functioning brain and moral center, if he secures the nomination, it becomes very hard to predict what states are on or off the board for the GOP, and if he loses the nomination makes good on his threat to run independent? We probably see the greatest landslide since the 80s, Texas turns blue in that situation.

But it doesn't happen if you don't vote, and that is what the Republican party is counting on, disaffected liberals driving down turnout, their base is motivated and can be counted on for solid support, ours is not so much, there are more of us than them, we can make a difference in our fates, if we actually go out and participate a bit.