This is a nice little video from Golf Channel's Playing Lessons with the Pros where 3-time major golf champion, Padraig Harrington, talks about creating power in his swing. Obviously, the baseball and golf swings are different, but basic principles of movement apply to both - things like stability (on the back leg), rotation, connection (although I typically think or talk about it in the forward swing for baseball rather than the back swing) and the kinetic link.
The good stuff starts around the 13:10 mark...
[caption id="attachment_2857" align="aligncenter" width="309" caption="the Happy Gilmore drill"][/caption]
Harrington talks about turn/twist/rotate through to impact, which is a concept or explanation that sometimes gets a bad rap in baseball because of players' tendency to drag the bat or spin on the back foot when focusing on rotation. The baseball swing has a quickness component that doesn't exist in golf, but even in golf it is possible to drag/cast the club. Golfers, however, typically try to maintain a "hinge" angle or prevent the club from casting too soon in order to save up all the rotational energy and release at the last possible moment upon contact. This way they can create a lot of power through their rotation AND be in position to transfer it to the club right before contact.....this can't happen in baseball or golf if you're dragging the club/bat.
And of course, there is the Happy Gilmore drill (hard to spin on the back foot doing this one!) where Harrington talks about taking a step as in a baseball swing, and how he uses it to create EXTRA power. This would typically be seen in baseball in a common drill called the walk-up drill. Remember, the idea is to take the lateral momentum and then use it to ADD to what Harrington described as turning/twisting/rotating into contact. The big lateral shift is relatively worthless (think sliding or lunging) if it's not converted into rotation.
Here's a little more from Sports Science: