This is my list of important election between now and November.

March 4, Italy

An opinion poll by EMG Acqua from early December suggested that no one party would gain a majority of the votes, creating a "hung parliament" situation.

If the polls are correct then nothing much will be decided in March.
The most likely winner is the center-right coalition. Although if the populist Five Star Movement (which is the most popular party in Italy) does better than expected, then anything is possible. The reason being is that the far-right Northern League and Five Star are Euro-skeptics.
Any move away from the Euro currency could cause a panic in the financial markets.

July 1, Mexico

Unlike the Italian elections, the likely results of the Mexico elections could be earth-shattering.

Andrés Manuel López Obrador's campaign rhetoric can make him sound like a Mexican Donald Trump.
The left-leaning front-runner in Mexico’s presidential race is overtly nationalistic, pushes “Mexican people first” policies and peppers his speeches with anti-establishment slogans that thrill the working-class Mexicans who flock to his rallies.
But while his style might be distinctly Trumpian, his policy prescriptions could not be more different. Indeed, the election of the former mayor of Mexico City could be disastrous for Trump and his administration, creating an even more charged relationship between the two countries that could reduce cooperation on border security, trade and immigration.

Socialist Obrador, who has made fighting corruption central to his campaign, leads in the polls by as much as 11 points. If his lead holds it is likely that Trump's diplomatic relations with Mexico would virtually collapse, with unknown consequences for NAFTA negotiations.
As if to underscore how serious the establishment is taking this election, the U.S. is already blaming Russia.

May 27, Colombia

Colombian presidential elections used to be about defending the country from leftists, not bringing them to the threshold of power.
Next year’s vote, the first since the end of a five-decade civil war, may be different. Ahead in recent opinion polls is Gustavo Petro, ex-mayor of the capital Bogota and a former guerrilla who’s promising to tax wealthy landowners and stock investors. He’s battling for pole position with two pro-business candidates, while other left-wingers also feature among the early frontrunners.

Colombia is a relatively small nation, so it's impact will be marginal but symbolic.

Various Democratic Party primaries

The sheer, historic volume of candidates, particularly among Democrats, tells part of the tale. The surge is most apparent in contests for the House of Representatives, where, through the end of September, 455 Democratic challengers had already registered with the Federal Election Commission — more than twice as many than at any other point in the last 15 years, according to an analysis by the Campaign Finance Institute. By comparison, only 111 Republican challengers had filed to raise money.

This year will be the first real test of the ability of the progressive left to knock off establishment incumbents.
Unfortunately, most of the races, especially in the House and state level races, haven't had any polls done yet. Even the polls that have been done often exclude first-time challengers.
So it's impossible to guess which might flip at this point.
However, there is an exception.

No state democratic party is a bigger enemy of progressives than Florida, but with the influx of refugees from Puerto Rico that could change at the governor's mansion.

The Democratic primary has no clear frontrunner but no shortage of candidates, with a field that already includes former U.S. Rep. Gwen Graham, former Miami Beach Mayor Philip Levine, businessman Chris King, and Tallahassee Mayor Andrew Gillum, an African-American who's running from the left by backing Medicare for All and action on climate change. Personal injury lawyer, medical marijuana advocate, and living-wage proponent John Morgan is considering running as well.