I've heard good things about Dan's Whetstone which can be found at
http:danswhetstone.com
Dan seems to have a better selection of natural Arkansas stones than any other place I've found.
I'm about to order a 8" hard Arkansas (extra fine) from him, I'm just trying to decide if I go hard black or translucent, and whether to get the 1/2" thick or the 1" thick model.
As to DMT, I've also looked at and like the DMT Duo Stone. An 8" model can be had with coarse (360 grit) on one side and fine (600 grit) on the other side for around $100.00. DMT uses mono-crystaline diamonds which are suposed to past longer than most of the other diamond sharpeners on the market. For smaller and less expensive, the Duo Fold, the double sided one Kwaiken mentioned, is available at less than $40.00. I'd get one in coarse/fine as 360/ 600 grit is way more useful than the 600/ 1200 grit model he posted about. A 1200 grit stone is for a much finer polished edge than most folks need for everyway use. It's much more useful to have a 360 grit (not really coarse in my opinion, more like medium) to smooth out or mildly re-profile an edge and then finish it off with 600 grit. If you aren't pretty good at freehand sharpening already, a 1200 grit stone is almost useless.
I also can't recommend the Spyderco Sharpmaker 204 enough. While I've been freehand sharpening for a couple decades now and was taught by a decent knifemaker, I use the 204 for most of my daily maintainance these days. I'm looking for the new extra fine stone to go that last step after the 204.
Remember, these are only my opinions.
jmx