If your looking for a natural finishing stone, the choices are somewhat limited. there's the aformentioned belgian yellow coticule. there's the escher/thuringian stones (eschers are probably a bit better, but are costly. on the other hand thuringens are easier to find and cheaper). then theres the whole world of japanese waterstones, but thats opening up a whole can of confusing

don't forget that shapton makes a few different lines of stones, most ppl only consider the pro series. they also have the M15 series which feels more like a natural stone (softer and makes a slurry) and goes as fine as 12000

theres the 8000 kitayama (similar to the yellow coticule in that it leaves a finish closer to 12000). there's also the ice bear 10000 and naniwa 10000

Want a quality tool that gives some great edges at a fraction of the cost? Buy my Tony Miller 2" pasted paddle strop (1.0 micron/0.5 chromium oxide) for $40

Look at that, a convenient link:

http://straightrazorpalace.com/showthread.php?t=13607