I was sitting in history today learning about the ancient macedonians, and an idea came to mind. Group attacks/formations, like a phalanx. Your shield would protect you, and the person next to you. Getting a group of spear-toting warriors lined up would be cool. =) Also, some other ideas to come out of history class, what about siege equipment? (I know this has been briefly discussed elsewhere, but I want to echo the idea because I realy like it.) Balistas, Catapults, Trbuchets, Siege towers, Battering rams, Mobile ladders, etc. Probably a bit complex, but would add a lot to guild vs. guild, or Kingdom vs. Kingdom combat. I have never heard of MMORPGs where Wars have broken out. Like hundreds fighting hundreds for the glory of their Kingdom/city-state/whatever. Okay, yes, that would be laggy for anyone without T3 access and a P4 3.0ghz comp (minor side effect =P), but it would be unprecidented.
Another thought that came up was Calvalry(sp?). It has been mentioned before, but land based mounts were never discussed. Land based mounts would be very nice for those that need to travel long distances, but have no access to a flying mount. And once on the surface, would boats, or water based mounts become available? Anyways, just a few more of my random ideas.