Hippo does this, but only with Mpeg2 all-i frame movies. They actually do some interframe interpolation. Maxxedia does this, but not with quicktime files. Mbox does this with quicktime files (frame blended playback). They all work quite well.
The hippo and Maxxedia do it better, but you have to have very specific file types. The Mbox might not be as good, but it is normally enough to get you where you need to be, and it works with all videos that the mbox can play back.
As a side note, this would be extremely useful in pixelmapping applications, as getting slow enough movement when your pixels are as big as 1 foot is very difficult.