I agree with Mike that a bow saw is easy to use. However, if you have a lot of wood to cut, I find that an electric chain saw works extremely well. It is quiet, easy to use, and inexpensive. You can get one with a 16 inch blade for somewhere in the $75 to $99 range.And you do not have to mess with gasoline and oil.
Currently I have a lot of pecan that is 4 to 8 inches in diameter. I cut my pieces into 3 inch long rounds, let them season, and then I use a hatchet to split the rounds. I place the hatchet on the wood and hit the hatchet with a large rubber mallet. This way I control the size of the chunks I get (sometimes I want smaller chunks to use on my Genesis grill).
Hope this helps,
Ray