A while ago I mentioned that I'd been testing a sample of a new diamond abrasive product but I can't remember where, so I thought I'd mention it. I got mine last year and am really impressed with it. ChefKnivesToGo will soon have the stuff in many sizes and grits. The stuff I have is 125 grit and really amazing; there'll be one that's even coarser but also as fine as 0.1 micron (yeah, a tenth of a micron!) if you want to take it that high.
I have no affiliation with the product beyond being fortunate enough to "beta test" it. But I'll certainly be buying some more!