Well, let's see...
The straight grip is like what you see on most longbows. A straight/flat handle with no curves to it.
The low/med/high wrist grips are normally found on recurve or pistol grip bows but you could use the same concept on a straight grip. This type of grip has to do with the position of your wrist and how much the grip is built up. With a low wrist grip your hand it almost at a right angle to your arm, so your wrist is low. With the medium grip your hand in at a 45 degree angle to the bow handle so your wrist is in a medium position. With the high wrist grip your hand and arm are pretty much form a straight line so your wrist is in a high position. Most production bows come with a low wrist, or #1 grip.
This is a #1 or low wrist grip:
This is a #2 or medium wrist grip, notice how the grip is built up so that the angle is sharper:
I couldn't find a high wrist example.
A locator grip is a grip with something added or cut out of it to help you "locate" your hand in the same place and position each time. A pistol grip is a kind of locator grip. Mike Fedora adds a locator bump to most of his bows to help with consistent hand location.
The only other grip variation that I can think of is that some bowyers will build out the handle to form a palm swell which some folks like because it causes them to rotate their arm some and helps with a high wrist grip. Black Widow Bows calls this their Asbell grip.
Hope this helps,
Snakeeater