One way if you don't need slices would be to use the rectangular marquee tool set to a fixed
size (200 px X 200 px) and divide the image into layers and then use File>Scripts>Export Layers to Files.
What version of photoshop and what file format do you need?
CS5 png. The problem is I will use it often on that file, make some changes later and then save it once again. Dividing image with fixed rectangulars sounds like repeating process. So basically slices are great because they stay in a file forever in the same position.
I've got some idea of using rectangulars as placeholders for further divide, so when I update the file I would use some action to copy everything what's underneath into layers and then export. But still, some of the manual work here...
There used to be a script somewhere that was able to fake multiple slice sets by storing additional info in the files metadata and then running the script to switch sets. Maybe do a search on that...