On July 4th, 2012, CERN announced that, using the Large Hadron Collider they found a boson particle that so far is consistent with the Higgs boson. It will take ages of further testing to figure out whether this boson is actually a Higgs boson, but this is a very promising first step, as it is the first boson ever observed.
The Higgs boson, and the boson field associated with it, can help to explain why matter is affected by gravity. This would be a huge step in our understanding of the universe, and is probably the last step in completing our understanding of the standard model of particle physics.
To find out what a Higgs boson is, check out this excellent video by PhD Comics.
For a briefer overview on the Higgs boson,... keep reading