Rudy Project's Crossway Helmet is a lightweight, well-ventilated option for XC and Trail riding. Check out our review to see how it compares to the competition, and if it'd make sense for you.
Fox’s Speedframe Pro is a high-end, broad-coverage Trail / Enduro helmet with a 5-star safety rating from Virginia Tech. And given its solid coverage, it's also been very impressive in terms of ventilation for hot rides. Check out our full review for more, including several comparisons to its competition.