Well bike helmets haven't changed much in years, but the latest improvement is in reducing rotation forces. The EPS foam in most helmets works fine for crushes, but most accidents cause your head to spin which ain't so great for the Mark 1 Brain.
The solution is a little piece of plastic that MIPS licenses to helmets companies for about $20. This really does seem to work. If you look at the top independently rated (by Virginia Tech). MIPS has the top one and most of the rest.
There are other technologies out there and Trek through it's Bontrager brand has the rights to a technology made by a Portland, Oregon company. They've made some bold claims (which MIPS of course contests), but it is out there as well now and they do hold the #2 and #4 spots on the list.
It's also interesting to see that cost and protection are not really correlated. I think we've all suspected that the $300 helmet is more about marketing and losing a few ounces than real protection. The fact that an obsolete $75 helmet, the Lazer Cyclone MIPS, can beat all the other helmets is probably an indication. But overall, getting one of the top ones doesn't seem like a bad idea for everyone.