Media Player Classic is love. Aside from having an actual good built-in screen capture function, it also lets you watch things speeded up or slowed down, which ALSO helps with screencapping -- speed up to find the scene you wanted to cap, slow down to make it easier to find the exact moment -- and even a frame-by-frame advance, which is even better.

http://sourceforge.net/project/showfiles.php?group_id=82303