If you look down the list here
, you can see how the base damage jumps up dramatically at early points there. Around 30, you're right, Voulge or Centurion's would be a fine choice to jump up from ~40 damage to ~50. Then again you see a jump at 37 with the Horror Voulge to 60 base damage. There are some good options in the mid-40s, though your real leap comes around 50 - Gigant Axe at 49 at 75DMG, though at 50 Leocus Voulge bumps things all the way up to ~80DMG. You don't see much better for overall DPS until the later 50s/early 60s - IMO, just go with whatever is decent and cheap/easy, you won't be sticking with them for too long, and any pricier low/mid level weapon will be a **** to unload once you've outgrown it. Berserker's Axe at 69 is cheaper now, and will be a good pick until you get a Rare/Ex weapon (NM drop or Magian).
A consideration later on is that the "highest" DPS weapon might not be what favors your setup the most. It's a lot easier to build for a 6-hit setup on a 504 delay greataxe than a 488 or 482 or whatnot. Edited, Nov 5th 2010 1:33pm by Isiolia