From New Scientist: Did dark energy give us our cosmos?
This theory puts together a couple of my favorite ideas. First, in M theory, our universe is just a part of a larger structure. The article talks about it "exists on a 3D region called a 'brane' separated from similar branes by a fourth spatial dimension." Sometimes, these branes collide, causing something like the big bang. Next, the universe is in a never-ending cycle of bang, expansion, and then contraction. (I like this because not only does it answer the question of what came before the big bang, but it also eliminates eternal expansion and eternal death of heat, light, etc., which scares me in a way it shouldn't considering I won't live that long.)
The problem with this idea is that all the different parts of the extended 'verse would have to move to fit expanding and contracting branes, so "large areas of the brane become warped, so that most of it ends up as black holes and only a tiny proportion as ordinary, habitable space." But! Add the element of dominant, pervasive dark matter, and the theory starts to come together. Sweet.