Depending on the brand and model, you can get high gain antennas that increase range. You could also do something as simple as putting the router on a shelf WAY up near the ceiling, which could give you plenty of extra range all by itself. I personally don't like ANY of the "internal antenna" wireless routers on the market particularly because they are hellishly hard to tweak for coverage area, while external antenna models make it pretty simple, especially the dual antenna varieties.
A "draft N" router may give you more range, but remember that it's still "draft" and there's no guarantee that the final spec (and hardware that comes out meeting that spec) will work at all with the current draft equipment.