I like the look of those flat waterstone grinders. Though it looks like Rutlands aren't currently stocking them as that link is for the planer blade jig, and not the machine. I'm not sure about that one from Dictum as it looks like you wouldn't be able to flatten chisels/plane irons on it as the stone sits below the lip (but maybe I have this wrong). If anyone can correct me on that, please do as I might consider one in the future.
I had a Worksharp 3000 and really liked it. I sold it and wished I hadn't! The only issue with them is that the consumables are stupidly expensive, but they work really well and are great for flattening. It doesn't overheat the steel easily unless you're really taking a lot of metal off and you can always dip in water. I'm considering getting another if and when funds allow. Though you really need the few extra jigs (platform and rail) for making a truly versatile system and that really takes the price up (unless you want to make the MDF platform that StumpNubs describes).