I'm using hexes. I prefer the more 'organic' feel it gives compared to squares.
http://www.d20srd.org/srd/variant/adventuring/hexGrid.htm - not for 4e, but it should give you a pretty good set of ideas from what you might want to use.
My current plan is to make blasts cones with distance equal to the number of squares, so Close Blast 3 = 15' cone. It'll change the effectiveness a bit, but it's going to be across the board, so I don't see it really hurting the pcs too much. This may be on a case by case basis, probably done on flavor.
Bursts will remain unchanged, aside from being hexes. I haven't made my mind up on what I'm doing with wall effects yet. I might reduce the effect number by 2 or something...or I might just leave them alone until I decide.