Yeah odd grid patterns are fun to think about. As mentioned before as a joke, you could use an octagonal grid:
Where Octagons are for creatures, and the squares could be spell effect centers or Ethereal travel...
or you could use the Dodecagonal grid also mentioned as a joke:
You could use the triangles the same way as the squares in the example above. The cool part about these grids is that they let you use the other rules for square or hex grids, respectively.
Not sure if this would actually be useful, but it's fun to play with.
Edit: And to respond more directly to the OP, I like hexes on a purely emotional level. They're cool looking, and the straight edge issue doesn't apply to me, since I can cut the hexes in half, or even say that two medium creatures can fit in a hex.
From a practical standpoint, squares are easier, since I like my 3d combat. I have half a notion about treating Hexes like cubes:
And figuring out how to read the hex grid such that movement would make sense. I've tried before, but it didn't seem possible. I think you'd have to focus on the diamonds, and use an isometric way of viewing the map.
