How can I cut lots of cherry tomatoes in half quickly and evenly? Is there a tool to cut cherry tomatoes in half? Since they are so regular it should be possible to build such a machine. 

Alternately, what can I do to improve my speed and accuracy when halving them with a knife?
Yes there is. It's called a knife. I use a Shun 10" chef's knife, but you could certainly make do with a much cheaper one.