One very unique game is Hordes of the Things, it is an extremely generic fantasy rules set that can allow you to make pretty much any army you want and can be addapted to other periods. They do this by having generic unit types almost anything can fit into, unit types like Blades, Spears, Heros, Riders, Wizards, Flyers, ect. (21 types in all). You can make almost anything , I have seen general fantasy armys (elves, dwarves, knights, ect.), rock armys (
http://www.matakishi.com/15mmrockarmy.htm), a Doctor Who army, and many other great and funny armys. The game can also be played in any size you want: 6mm, 15mm, 20mm, and 25mm ( I have made up my own sizes for 28mm, 25 is a little small, ask if you want it). The rules are relatively simple, but the game is still very strategic.
The rules are avalible free online, at this site:
http://www.wrg.me.uk/
(There is a link to the rules about halfway down the page of "History of W.R.G.")
The only problem is that the origional rulebook is a bit hard to understand, but you can get a helpful reference sheet here:
http://www.panix.com/~sos/mini/hott-aid.html
(Link to pdf. at top of page)